Life changes certainly. It depends on how you let it affect you.
Main pros of age:
-Independance (you can do what you want within reason)
-Additional skills/life options open up (for example, you can't even start learning to drive a car in the UK until you're 17)
-You gain more experience/knowledge (My dad is 50 something and he and his brother can damn near build a house themselves. He couldn't do that when he was 20)
Main cons of age:
-Independance (Your parents can no longer protect you from lifes difficulties as well as they used to. Hopefully it sounds like you'll always have your partner to rely on instead)
-Financial responsibilty (Don't listen to those who say money is everything. Yes, having more money is nice but just because you can't afford that Ferarri Enzo doesn't mean your life is a failure. You can still have a damn good car and be happy. Same applies to other things. I earn the national minimum wage and I still have the economic freedom to do most of the things I want to do if I'm careful with my money)
-Eventual physical decline (If you work out and maintain your body they you really enter your physical peak in your 20s and keep at it you will keep that well into later life. In the last couple of decades of life though your physical and possibly mental faculties will start to decline if even by a little bit. You can still be happy though.)
So life changes. If you can't cope then you will struggle but plan ahead, look after yourself and those you care about and enjoy what you have rather than lamenting what you can't have and you'll find that some things do get better with age