… your period has stopped but you’ve grown a mustache.
… your mouth starts to look like a drawstring purse.
… medical providers go from asking you the date of your last period to asking if you’re still having one.
Your rear and your breasts are almost the same height.
I’ve noticed my hands are starting to look like my mother’s hands. I kind of like it so far.
And yes, the menopause thing–I had an ultrasound on my kidneys recently, and the tech asked if I was in menopause. I had no idea–I take continuous does birth control and haven’t had a period in almost a year. I never even considered it, but I guess I should since I’m 48…
You stop seeing your mother in the mirror and start seeing your grandmother.
One way to tell is to notice if you’re using the air conditioner in January.
Nice, people!
… you plan getting up from whatever position you’re in.
What’s scary about this is it happened to me when I was about 26, altho the grandmother I saw looking back was from a photo of her when she was young, so that’s not too terrible, I guess.
As for me, the smack-upside-the-head sign of my aging was when I needed to get trifocals. And when I take them off, everything’s a blur - I can’t even watch TV without them any more.
Thanks to genetics, my hair still has no gray, and thanks to extra weight, I have few wrinkles. I do see lots of “age spots” on my arms, and sometimes my fingers are really stiff, but overall for a 58-y/o, I’m doing pretty well.
We won’t talk about my memory…
. . . people stop telling you you’re good looking, and instead tell you you’re looking good.
Y’know… you are lookin’ good these days. 
… you say something like, Oh, I’m too old for that, ha ha.
And it is met with utter silence.
My fat used to go to my boobs and behind, now it goes to my belly.
TV characters that used to look really old? not so much.
this morning I was working out and found My Three Sons on TV. Uncle Charlie was trying to get a date but the waitress at the coffee shop wasn’t interested and I found myself thinking… he doesn’t look so bad…
You start buying underwear for comfort, not how cute they are. 
While in the shower you start using hair conditioner on your pubic hair to make it feel soft again.
You look at pictures of your mom when she was in her 20’s and think “Oh my god she’s such a girl right there!” and then realize you’re more than twice her then-age.
(Actually I got a big hit of that when I reviewed pictures of my mom, with me at six months old. My mom was already back to a perfect sexy figure; so jealous! I don’t even have kids and I didn’t look that good! Go Mom!!)
Your knees start hurting for no reason.
I can handle my knees hurting because I tripped, or twisted funny, or fell, or ran too much or otherwise injured them. But when my left knee ached for a week this month for no reason whatsoever…yeah, I’m gettin’ old.
… any little glitch at all and you think it’s dementia. 
…ALL your body hair starts turning gray.
…your joints take turns hurting.
…you pray for menopause so this fertility cycle crap will finally just stop.
Some days I am so pissed that I have wrinkles and acne, am pre-menopausal and PMSing, and am half gray with an oily T zone.
…you find your first gray eyebrow hair. :dubious:
…you find your first gray pubic hair. :o
…you find your first gray mustache hair. :eek:
…you decide not to wear lipstick anymore because it feathers out into the fine lines around your lips.
…the back of your hands start to look like Sarah Jessica Parker’s.
…when you kneel down, your husband laughs at you because your knees go off like a double-barreled shotgun. Kapow, Kapow!
This. So very this. No matter how my weight fluctuated, my proportions were always downright Betty Boop-ish, but these days I have to be very faithful about doing my core exercises and careful about what I’m eating, because every ounce of fat and water wants to wrap itself around my waist.
On the non-physical side, I’ve officially reached the point where everyone I meet reminds me of someone I already know. I’ve seen all the faces and met all the types. On the bright side, it’s a time-saver.