I think you can't automatically pre-judge someone until you've actually spent time with the person...I'm 25 and have been told by 90% of my clients that my maturity level is that of someone in their 30's-40's.....Just as there are young girls who are immature, there are also plenty of "Mature" providers that act like drama queens.
I feel like a lot of one's maturity is based on their life experiences, so my advice is to stay open-minded. If there's a younger provider that you fancy, get a feel for her (no pun intended) and trust your instinct, but I wouldn't rule anything out...
Val