In my 20s, I dated casually, had fun, didn't think much about the future. In my 30s, everything changed. Suddenly everyone seemed to want serious relationships or was already married.
People are more set in their ways. They've learned from past relationships. Either they've done the work to grow, or they haven't. Learn to spot the difference.
The Advantages
You know yourself better. You know what you want. You're usually more financially stable. These are huge advantages in relationships.