Break the promise?

I've made a promise to myself that I'm not going to be in a relationship till I'm 20 years old.
Why? Because I don't want to get hurt like I've been in the last few years.

I want a partner, but everyone in my age or above is either a player or is too immature.

But this last month, I have been with my friend Stefan allot. And I've started to like him allot. And I think he feels the same for me. We have been friends for a while, so I know I can trust him.
But I'm still afraid to be in a relationship.

So that's what stopping me now too be in a relationship.
But I still don't want too loose him. Cause we get along so well. So I don't know what too do.. Should I break the promise to myself, or should I stay with it and maybe loose Stefan?

Question; What would you have done?

-J