That first gray hair is definitely a bit discombombulating. Something that I find worth remembering is this: if you're in your early to mid twenties you almost certainly have two literal entire lifetimes worth of time left to do stuff in. The time will not be the same as your early years, but you trade youthful exuberance and (some) energy for experience and wisdom. It is not a bad trade. You can do some really cool things with the abilities you develop as you get older.
For a while I lamented the loss of previous opportunities. I think many (all?) people do this, and part of the reason is a natural human tendency. Another part is the tendency of older generations to tell kids "your opportunities are endless." It's nothing against them because it is true as far as it goes, but the part they forget to mention is that as time goes on you HAVE TO and WILL solidify choices in history, and that changes your possible trajectories. That is how time works. I haven't figured out a way around it, and lacking a time machine I doubt anyone else has either. Your recognition that you could one day wake up in your 50s and lament the loss of your 20s is a useful tool for making sure you don't actually waste them. Once you get there, though, just remember that whatever you are doing now is what you wanted to do (bound by what you are able to do, of course). Nothing is perfect, and it's important to know that you do forge your own future.
Just my two cents. I hope it's helpful for you. We are all playing on the same game board, and I wish you luck with your game.