@Adam Rose, I think it's great that you're even having this question/dilemma at your age. If I had it at your age (and I wish I had), I'd be in a LOT different place now. Allow me to give you a few bits of advice (about which I speak from experience):
- you don't want to be 'stuck' in career
- if your going to do REI, start as early as possible (but don't rush!)
- don't exclude the possibility of doing both simultaneously (rather than alternately or either/or)
there are some really good points made thus far in this thread: i especially like the 'good neighbor' thing and I'm a huge fan of house hacking.
Imo, @Melroy D'Souza has the same short answer/advice that I do.
My short answer is: become a cop and house hack. See how both those situations work out for you and go from there.
My long answer would also include: enroll in the academy when you can and buy a duplex when you can. look into the HUD Good Neighbor Next Door thing and determine if you'd rather wait to find a property that fits that (and wait till you're qualified) or just jump on a good deal you find.
I have a friend who went from mechanic to cop, then to cop/landlord, and now is house hacking, has a 4plex, and works for the state law enforcement. he says he'll never quit his W2 because he loves his job, but he also says he'll never quit buy and hold either. his REI really is a part-time thing (even though at times landlording can be full-time-ish).
However you decide to play this out, I wish you the best of luck!