I’m getting creaky.

And, goddamn, it’s really throwing a wrench in my self-perceived invincibility. It feels like just yesterday I was climbing trees ’til the branches snapped beneath me, jumping to the ground from 15 feet up knowing that my knees would simply absorb the impact, like putty, or pillows or something equally cushy. I was running around without even the slightest thought of sunburn, or suntan or sun block, and my dad scooped me tureens of ice cream, the volumes of which make the new dining hall bowls look doll-sized in comparison.

I fell, I got up. I ate, I metabolized. I made mental notes, and I remembered them. Whatever in the world I happened to do, the next day I would bounce out of bed without the slightest soreness, struggle or unprompted salivation. All this, well — all this has changed.

What happened? Where went my prior immortality? Ancient asthma is kicking back in when I sprint on the soccer field, and the dormant scar across my leg recently inflamed from sun exposure, or something. My eyesight is growing steadily worse to the point that wearing my old glasses leaves me massaging my sockets in agony. Food gets stuck in my teeth and it just kind of stays there, until I throw a glance in the mirror and notice my gums have become a collage of foodstuffs. Thirty minutes in medium sunlight has me pinkling like some pseudo Peking lobster rather than slowly roasting like salted honey almonds, the way I once used to. I’m half Asian. As in, like, some natural variation of yellow. Come on! Sunburn isn’t supposed to be part of my genetic makeup. But lately? Oh, burn baby burn. I’m pretty sure I glimpsed a few sunspots on my upper arms, but I’m too scared to look again.

I turned 20 almost a year ago, though I thought little of it. The banter around the double decade mark is painfully banal: “What happens when you turn 20 years old?” someone asked on Yahoo! Answers. Well, my friend, what do you think? I liked this response: “Your bones will turn to dust and kids will call you ‘Ma’am’ and ‘Sir.’” Spot on.

But no really, I think my bones are headed in that direction. I don’t think I knew what sore was before the age of 18, no matter how many books I carried in my backpack, how many suicides were run at practice, or how many plastic saucers I broke upon impact after plummeting back to cold, hard, snowy earth off an overambitious jump. Another respondent chimed in on the Yahoo! forum: “There’s no way really to feel, just a year older. Things will be the same.”

Things will not be the same! And you, you going on about how “You will no longer be a teenager which is a cool thing I guess” — there is nothing cool about suffering a back spasm as you try to get out of bed, only to find that your lower left hamstring is throbbing but you didn’t even exercise yesterday so what could it even be from? Or trying to slip on a flip-flop when suddenly your fourth toe cramps, incapacitating you from any further movement and sending excruciating pain shooting up your foot. Or staring at a pair of twin babies in a stroller while you’re slobbering on an immoderate ice cream cone, conscious with every lick that this triple fudge moose tracks diddly doo marshmallow nut swirl beepbop coffee chip java chunk is going to take a little more than a game of freeze tag to wrestle off.

Oh — and wrinkles. Don’t let me forget wrinkles. Pretty sure those are happening too.

“14. Get a six pack (or get thin) while you are young.” This was one of the recommended “20 Things I Should Have Known at 20” I discovered on an online blog. The list’s creator, Julien Smith, pointed out the grim reality that “your hormones are in a better place to help you do this at a younger age.” He might also have mentioned it will be easier to get up from the crunches on the ground now, rather than later. “17. Get a reminder app for everything. Do not trust your own brain for your memory.” This is consoling. I leave my iPhone on toilet paper dispensers and can’t keep track of a water bottle or scarf for more than three days. I write things in pen on my hand, forget to look at my hand, forget to shower, eventually shower, and then can’t decipher what was on my hand, besides remembering it was really important and time-sensitive.

“9. You will become more conservative over time. Do your craziest stuff NOW.” It’s true. I consider leaving my room after 11 p.m. on a Saturday night a praiseworthy effort, mostly because I don’t want to put myself through anything that will have me spasming, rather than bouncing, out of bed the next morning. Tip 9 brought to mind a line I read in a book called “Brandwashed” by marketing guru Martin Lindstrom: “Our ‘window of openness’ for new experiences, like getting our tongue pierced, slams shut at age 23,” he says. I used to think this sort of suggestion was ridiculous. What do you mean I won’t still want to jump off cliffs and compete in Tough Mudders and get debilitatingly drunk? I always saw myself as that grandma, the one who took you sky diving for your 17th birthday (yeah, that’s a type of grandma, and I’m gonna be her). I’m not so sure now.

So I’m getting a little creaky, a little crumbly, a little kooky. So it goes, so it goes. Twenty-somethings, we’re not going to bounce back like Slinkies forever. I guess the bottom line is this: when adventure comes a-knocking, we gotta toss down our problem sets and papers and get out there while we’re still rearing to go. When Grandma invites us skydiving, we give an unequivocal yes, even if she schedules it during finals. And, if we’re ever so lucky, we’ll be inviting our grandchildren to do the same. Or just driving them up East Rock. That works too.