I am officially old and have lost my perspective from youth. I got married at 18 to a man a met when I was 16. He is 12 years older than me. I know I sound like an asshole who is judging you for being young and wanting to have fun and talking about marriage. It sort of blow my mind that a post like that just came out of my head. Discard that if it feels like an old person telling you you don't know what love is and let me offer this.
I'm still married, 12 years next monday. I feel like I got super lucky with the choices I made. I didn't know everything about myself then but I ended up with someone who loves who I became. Thats got to be part luck. I never wanted to be 20 though. I'm in the same line of work now as I was when I was 20, we bought a house that year. I never wanted those experiences you've described so I don't feel like I missed anything. I never felt a big maturity or generational or stage of life and interests gap with my husband. When I met someone else I fell in love with I never once fantasized about a life with the other guy without him in it. I never thought about leaving him.
So let me take back saying don't think about forever, but just remember you don't have to think about forever for it to be love now. Enjoy life right now.