 Weird things that'll happen to your body in your 20s, 30s, and 40s. Yeah. 25% of guys start losing their hair by age 21. Your wisdom teeth have likely already grown too big for your skull, and you'll need to get them removed to avoid infection or damage. Don't get too attached to those muscles. You start to lose muscle mass at a rate of about 3-5% per decade starting now. Also, your brain starts literally getting stuck in its ways, being less able to fluidly problem solve, and you start relying more on things you already know. The lens of your healthy, squishy eye starts to harden, meaning it's time to break out those reading glasses. Also, your lungs start losing their stretchiness, causing your airways to literally shrink. So yeah, you truly do start dying from the moment you're born.