Of course you can! I miss not being born rich just about every day of my life.
I'm 46 and I've been married or in a live-in committed relationship since one month before my 19th birthday. I got pregnant one month after being married. I missed out on the frivolity of a single youth. I can count on one hand the number of guys I dated before I met my first husband, and he was actually only my second "serious" relationship, if that's not something to regret, I don't know what is.
I'm 46 and I've never lived on my own. I've been someone's wife/significant other/mother for more than half of my life. I know how I ended up here, and why, but the fact is the life choices I made forced me down certain paths that closed other doorways. If I had it to do over, I would have stayed completely single and traveled the world for a few years.
I wouldn't trade my son or current husband for the world, but there are plenty of things I look back on and have twinges of regret. And the question is, "What do you regret not doing at 21?"