It depends entirely on the maturity of the parties involved, it's not really an "older/younger" thing.

But generally, the less mature you are, the more a relationship is selfish, i.e. you want to be in a relationship for your personal advantage, i.e. "i get sex when I have a girlfriend". The more mature you get, the more relationships go into the direction of "I want to make the other person happy". You still get your sex or whatever other advantage of course, but it's much more fulfilling if you can actually give the other person what they need, and temporarily losing your personal benefit of the relationship doesn't cause immediate breakups.