I see you're getting a second opion....good for you :)
In case you are still reading this...I agree with the mom who said "braces are cheaper than therapy". He'll stop when he's good and ready.
I was 17 when I finally gave it up! For some reason, I just needed it to fall asleep. I have a friend that, at 29, still needs her thumb to fall asleep.
My mother gets so upset that I let my five year old suck her thumb as much as she wants....but, by my not making it a big deal, she needs it less and less. Now she only sucks it to fall asleep then it falls out as soon as she's asleep. She does have a slight over bite, but she still has all her baby teeth. I'm sure by the time she gets her permanent teeth, her need for the thumb will be quite minimal.