As someone who recently turned 31, I’ll be following this thread closely to see if anyone has good advice …
Awesome. I’d probably do the same.
I’d move in with some roommates to save money. Living alone was more luxurious, but really not worth all the extra money required.
I was really just getting on track when I turned 30 - finally getting into an actual career, married to my husband. It was a good time. I might’ve waited a year to have my firstborn so I could’ve had a bit longer to appreciate being married and childless, though I don’t think it’s possible to really appreciate that without, well, having had a kid. Plus, eventually it’ll be just me and my husband again (we’ll never be childless - just a much quieter house, which isn’t necessarily a good thing). So there’s really not much I absolutely wish I’d done differently.
I’m 30, and I’m reading this thread for the exact same reason.
At 30 I was about a year into a great job and just had a kid who has turned out great, so nothing I’d change there. I’d buy Microsoft (this was 1981) and sell all my options in2000 and retire early.
What mistakes I’ve made were made well before 30, but I’m not at all sure my life would have turned out better any other way.
Since I assume time-travely things like “buy Apple stock - no, it’s not overvalued” or “write the FCC to prevent the WTC and Pentagon suicide attacks from succeeding” are not what’s being asked…
…I would have gotten into shape sooner. It took me until nearly age 36, and seeing a similarly physiqued co-worker succumb to Type II Diabetes, to start watching what I eat and getting more exercise. I lost about 50 lbs. in 8 months and felt great. For a few years, at least. Then, when I turned 38 or 39, exercising felt like it just got a whole lot harder. Creaking knees, elbows, shoulders, etc., etc. I sure would have liked to have more years of feeling like I was in good working condition.
I would totally have divoced my woman (who was a pain in the ass even then) before I knocked her up. Would have stayed in the Army, done some deployment in Iraq/Afghanistan (like my comrades ended up doing), and then become a drill sergeant (a path recommended to me by my commander on more than one occasion).
So, anyone still in the service: dump your spouse, and listen to your commanding officer. 
For every person that says they should have done something different, I guarantee you there’s somebody else who did that thing at 30 and regrets it too.
Can we make it 24 instead, so I would have had the chance to write to Boston U asking “I asked you about PhDs in Chemistry and you sent me brochures for a double Masters’ in Chemical Engineering (MIT) and Business Management (Boston U) that I’d love to take but don’t think I can pay for… can you send me the information I initially asked for and/or on financing that double Masters’?” instead of going “
” and ticking them off my list of “places I’m trying to apply to”?
30 was the year that my employer and my lawyer decided it was “best for all intended” if I stopped working legally and moved to doing so illegally; it’s the year I moved back to Spain to help care for my dying father. While that was a big branching moment in my life, it came from the decisions of other people as much as from mine, and those of mine from which it came had taken place several years prior. As bad as some of the times back home were, I wouldn’t have stayed and worked illegally, no effing way.
I just completed my age-reversing device and am back to 30, but frankly I didn’t plan out the whole thing very well, so I’m also looking for advice.
30 would be no good to me. The worst year of my life but too late to change the things that caused it. Would also leave me in a nasty dilemma regarding the surprise baby I had with the wrong person. Going back I could stop that happening - but then I wouldn’t have my beautiful and amazing daughter, and that’s unthinkable. Nope. Thanks for the offer but I don’t want to touch 30 ever again.
You too? Mine would have been Sunday. Happy birthday. 
If I were thirty again, my wife and I had already had our first daughter, and had just found out (literally two days before my 30th b-day in December) that we were pregnant with another. Considering how things have turned out (happily married to an awesome wife, decent job, four kids), I probably wouldn’t change much.
If I knew then what I know now, I’d maybe do the following (all terribly dull and pragmatic):
[ul]
[li]On my 30th b-day: I’d have married my wife, so we could have had a tax break for the 2001 tax year (romantic, I know :rolleyes:). We married in 2002, after the second daughter was born - I just really don’t know why we didn’t get married earlier, especially since when we did get married, it was for the tax break.[/li]
[li]Mental note to future self: I’d have waited another year or so before buying our house (2005) - we were in an apartment at the time, and itching to get into a home. But we got what we could afford, a decent little three bedroom on a big lot with a great view - however, in 2006 we had our son, Kid #3, and things started getting cramped (Kid #4 this year didn’t help). Also in 2006, I got a new position that paid better money, and the housing market started tanking. So we could have had a much better house for the money if we’d waited, even if we’d still be underwater today.[/li]
[li]Mental note to future self: I’d have never bought our first minivan in 2005 (a year for bad decisions) - a used '98 Sienna we bought in from a Thomason used dealership. It had frame damage that eventually made it undriveable, but didn’t pop as totalled on the Carfax report. By then Thomason was out of business, so we were SOL.[/li][/ul]
Like I said, terribly dull and pragmatic. Now, if I were twenty all over again - holy crap would I have had some fun.
Gone back to college part time until I got a degree in anything that will open some doors for me.
And a tummy tuck after my second child was born.