Really work on my Chinese and Japanese and do more than just 5 years of Kenpo Karate.
Put to use my investment banking experience and REALLY make a pile of money. It would be sick and make George Soros look like a loser. leverage derivatives to the hilt and correctly ride a few bear and bull markets and select stocks.
Take earnings and make some really big real estate killings - of course keeping some select properties for myself.
Amen.
Just say no to the rods.
What in the hell were we thinking?
I would finally have enough nerve to talk to the girl I had a crush on 40 years ago, but found myself tongue-tied within 10 feet of her. Maybe I’d even ask her out. Wow – think of the good times I could show her!
Nah, too soon. Ask me again next year.
Knowing what I know now about women, I become Casanova II.
In the 1980s after becoming a wealthy baseball player, I buy hunting acreage and extend hunting invitations to George W. Bush and Dick Cheney. I make sure that plenty of alcohol is available.
Later, I spend a few days in LA before the OJ Simpson killing. I park a car outside Nicole’s house with a camcorder. I then follow OJ just before and after the killing and tape his every move.
On 9/10/01, I make a series of phone calls to airport security, the FBI, and anyone else I can think of.
First, I’d move out of my mom’s place as soon as possible, and tell my dad why so he could get custody of my sister and I then & there and I would tell my mom that the step father should beat her or us - and she should dump him then & there.
Second, I’d get my dad to get me tested so perhaps I could do grade 12 and graduate school asap - because I can’t imagine even knowing more being able to fit in any less than I did. I go to university so I could get a BSC by the time I was 17 or 18.
I would have to spend my teen years as a loner, because of the strangeness of myself in a teenage body.
As an adult I’d go out in search of those people who I had missed as friends due to not being who I was - and hope that the strangeness of the knowlege of the past still allows for those friendships.
That & I would save & invest some money so I wouldn’t have to struggle with money as much as I have in the past.
Either all that - or I would take a flying leap off a building & off myself there & then because even with the knowlege I have now - I could not stand being a teenager again.
There’s not much that I would do all that differently… I would maybe let my friends know more how much they meant to me. I’d be a bit nicer in general… I really was a jerk sometimes as a teen. I would have started excercising and watching what I ate more back then.
I think the biggest thing I wouldn’t have wasted my time pining so much over girls I would never get. A lot of wasted energy there that didn’t really help anything in the long run…
It would kill me to lose my kids. My daughter is 3 now, and if I went back in time she would never be born. Even if I met my wife earlier and had children with her, those would be different children, not my daughter. Conceive a child on a different day and you’ll have a different child, a brother or sister of the one you really had.
Going back would mean my daughter had essentially died. It would probably take years and years before I could get over the death of my children. Even if I was assured that my children still existed in the main timeline, I’d still be separated from them. Would a version of myself still exist in the other timeline, or would my kids lose their father?
I believe Nicole and ron would prefer that you park a car outside her house armed with a TASER.
Wonderful. Now I have to pull both you AND Bricker out of the the pokey. This will interfere with various of my evil plans.
I would rigorously follow the advice of Dr. Joycelyn Elders, the former Surgeon General. 
1971:
Be a lot nicer to my parents and siblings.
Work a lot harder in school.
Find a better hairstyle.
I would start playing guitar at 14 instead of waiting 'til I was 30.
Whenever I wasn’t playing guitar (or studying) I would be mowing lawns, shoveling snow, collecting returnable bottles etc. until I could buy a really nice pre-CBS Fender Stratocaster. I could have got one for about 250 bucks. (now selling for 25-30 grand and up) Then repeat as many times as possible.
I was wondering whether in this scenario you would have the same psyche you have now or you would have the immature, moody, and hormone-overwhelmed mindset you had at age 14.
In any case, this would put me back in 1979. I wouldn’t have much money to buy or do anything. The best I could do would be to convince my parents to invest in Microsoft.
As for bets, I’d wait another 11 years, go to Vegas, and put all my life’s savings on Buster Douglas over Mike Tyson. 
Ooh, a whole three years and a month.
This past year has been great, so I’d try not to change it too much. So the only class I’d try to test ahead in would be math. That and I’d take AP Chem instead of regular, though that’s a couple years away.
The only thing I’d want to change would be the crushes on girls I got. Of course, I’d get crushes on other people, but in this case, I’d choose the devil I don’t know.
I wouldn’t take the guys I took seriously, as seriously as I had. I would take some others a bit more seriously.
I would miss the smell of my children’s necks and the sound of their barefeet slapping on the floor.
I wouldn’t work as much after school, and I wouldn’t have moved out of my parents house (either time) before I was ready.
Advice that I would give a fourteen year old (1979) me:
Look, your father is a good and honorable man but like all of us he has his shortcomings, and all of those fights with your sister have left both him and Mom tired and unconfident about what they do know. Love him, but also reach out to others. You’re lonely, and as dumb as this may sound you need a few more adults in your life.
Ask that nosey neighbor if her husband could take you fishing sometime and hang out over there a little more. Tell her that you want to do better in football and that you want to go to college and let her be the pain in the behind that you will need to keep applying yourself.
Definitely ask Jimmy and Wayne’s Dad if you could go with them to church. Their religion will be more relevant to your life than any fundamentalist stuff that you hear about later. Ask him for a minimum wage job when he starts his business. It won’t go anywhere, but you will get more out of it than you will by sacking groceries.
By all means work with your Dad when he asks you to, and thank him now; don’t wait ten years to do it. If he shrugs it off that’s his problem, not yours.
Trust your instincts when you wonder if the plain stuff in life is really uncool. People sometimes act “really cool” because they don’t know how to do the day to day stuff, not because they’re above it. Sensible things are called that because they make sense, not because they’re boring.
The next decade will be a blast, but those years will mess with your head if you’re not careful. They may even if you are.
Beyond that, when a beautiful girl kisses you, then kiss her back. If she loves you, then love her back. She may deserve it, even if you can’t believe that you do, and you just might deserve it after all.
I’d invent the Rubic’s Cube and The Chip Clip then never work another day in my life.
Well, I might start up a little company named Google if I felt so inclined.
If it were just a few years earlier I’d give Bill Gates the start up cash he need so desprately way back when. Then I’d only ask for 5% of all future profits.
Now I know: “Shazzam!” is not a mispronunciation of the short-lived cartoon show about the genie Shazzan. I didn’t know about the Marvel family of superheroes, who got their powers by shouting “Shazzam!”, so when people said that word I thought they were mispeaking.
What I don’t know is how DC Comics ever let the producers of the genie show use such a similar name.
Ouch, 1973.
Assuming that I survive the devastation of realizing I’ll never see my children or grandchild (because knowing what I know now I wouldn’t be even vaguely attracted to their father and wouldn’t get knocked up at fifteen) again, I’d probably wangle fake ID to make me a few years older, take off and move to Oregon a whole lot earlier. I might go back to Cali long enough to see if my SO and I would still get along if I were a less damaged person–I think we’d probably still hit it off.
I’d have a whole lotta sex for about ten years, then back off before AIDS starts going around. I’d invest enough to make a good living without having to work unless I felt like it. I don’t think I’d be very happy, though, because I’d always be thinking of the life I didn’t get to finish and the people I’d be forced to never know because the circumstances wouldn’t put us where we needed to be in order to become friends. I think my karma would feel disarranged and wrong…
I’d travel a lot, especially before airport security becomes a total nightmare. I’d probably end up a crazy cat lady living on a big chunk of land in Oregon purchased before the real estate boom–I’d have lots of dogs and horses and other critters…
I just really don’t know if I’d be a functional person after losing my family to a haze of unrealized potentials…
“Replay” disturbed me greatly and still does every time I reread it.
Ow… I would SO hate being a teenager again!
I enjoyed my life back then (1988) but I was always reacting, not thinking. But now I understand myself oh so much better. If I could wake up tomorrow and the last 16 years were just a weird, but educational, dream I had I would be so much better prepared.
For starters I would choose not to go to high school a 90 minute bus ride away from my home. And most especially stop waiting for life to come to me.
Can we jump to 18? 14-18 were definitely the worst years of my life.
I might give dating my 10th-grade class neighbor a chance as part of the whole “being better equipped to deal with the shit I got at that point in life”. Back then, I said no because he was having a lot of problems at home (which everybody knew about), I was having a lot of problems at home (which people either didn’t know about or refused to believe), and the last thing I needed was to add his problems to mine.
there’s been other guys who tickled the back of my neck, but he just did it best… I’ve wondered more than once what else would he have liked to tickle…
14, eh? That takes us back into the Dark Ages of either 1995 or 1996, depending which particular date in my 14th year we’re talking about.
But you know what? I’m going to buck the trend here and say there really isn’t much I’d change. I did well in high school without having to study especially hard, I got to travel a fair bit (more than I’ve managed since), and I don’t have any girls I regret not going after.
The problem would be with me referencing TV Shows and Movies that haven’t been made yet (“What the hell are these Futurama and Family Guy shows you keep going on about? And this Matrix film?”)
I think the only thing I’m likely to change would be that, instead of moving straight Australia, I’d tell my younger self to take a couple of years off and go and see more of the world- travel through Europe and Africa, especially.
It’s only now (at 24) that I’m realising I’m unhappy because I’m not travelling, and it won’t be the end of the world if I take a few weeks off here and there to see more of the world.
And isn’t the OP exactly the same premise as the TV show Do Over?