I agree that it's not immature to know one's limitations, or how much we can handle for that matter. But to me, the reason those "limitations" are in place is because of immaturity. It would be interesting to hear others thoughts on this, but to me the reason I have those "limitations" are because i'm afraid of the hurt/mess, and because I really can be quite selfish at times. I see those characteristics as being immature. I don't know how others view that.
If we were discussing something more universally necessary, then I would say yes, we all need to make sure that we're ready, because un readiness = immaturity. But seeking a relationship that you don't really want that much sounds like a recipe for eventual apathy, a rushed decision, or even a marriage that dissolves after thirty seconds.