I would ask what they've been keeping her in, what she's been eating, how often she's been eating... I would also ask to take a look at the parents when you're over there. They are usually a good guage of how large their offspring are going to get (as well as getting a nice perspective on their size, care, etc). Maybe even ask to handle one of the parents just to get an idea of what an adult boa is going to be like. And take a good look at the baby before you take her home, make sure it's active, clean, bug-free, all that fun stuff...

I don't think it would be too early to get a boa. It's good to start out with a baby because you can then grow with the snake... you'll know it's temperaments, when it wants to be left alone and when it's all right to handle. As always, just make sure you do your research!

Boas are great snakes really... the babies can be a little nippy (though in my experience it's a rare few that are), but grow into stellar sweet adults with good care. I don't think you'll be disappointed.