Is friends with benefits dating is not suitable for people in deeper into twenties? For me, I would say no for sure. Because you have a point that you strongly agree with and you feel right in other aspects of life. In these aspects of your life, you may have a different perspective in that area, but you can accept it. Let it pass by the past. For me, I have some social perspectives. Everyone is the same. I think my social perspective is good, and I think my perspective is a vision of a better and more fulfilling world. But not everyone agrees with me, which is fine. They are my opinions, this is my life and I can accept it.
What I want to say is that I have thought deeply about what I believe, what I like, and what works for me. It took me to think about my beliefs and how it works in my life. The more I think about it, the more I realize that the choices I make are right for me, and not for others. But this does not solve your problem. This is more like a prelude to my answer. My answer is that it sounds like you know exactly what you want. In my opinion, you are very direct to him, and you are all very clear about your goals. No one deceives others, no one pretends, no one is hurt. Basically, in any kind of relationship, the other party is the only person who really matters.
There are other satisfying things. For example, being truly fully understood and seeing another person through love is a fulfilling mature hookup experience. Helping others in a profound and touching way is a fulfilling experience. Different people have different implementations. However, at its core, under all the surface and external things, our satisfaction is everything we have. If you achieve your satisfaction in a way that makes others' lives better, then you are doing a good thing. If you do it in a way that doesn't hurt anyone, then you are doing a good thing. Never let anyone or anything hinder your ability to get that satisfaction.
You are asking me if you are promiscuous. You are asking me if you are too old to try new relationships like fwb dating and nsa hookup. My answer is you are not. I bet that under these social fears, shame, guilt, or other feelings you want to call it, you know you are not. If you want friends with benefits dating, just go for it.