Recreational & Family - Trek Jet 20 for my son?

My son just this summer started enjoying riding. He wants a trek, since that's what I have. He is 50" tall and almost 9 years old. Is the Trek Jet 20 a good fit? If so, how many more inches until he needs a new bike?

I need to mention, I am 180 miles round trip from the closest bike shop and this bike is supposed to be a surprise.

No idea. I would really recommend taking him to go try it out, despite the hurdles. Pack him a large box with a picture of a bike on it or something for surprise, but get him a bike that fits. Returning it would be a PITA, if it's even possible. Make it a special trip with your kid to go pick it out, and use something other than the bike for the surprise. Or just don't tell him where you're going. Take him out to lunch and/or a movie, get a bike, have a blast.

My daughter was about that size (she has REALLY long legs) and we found her an xsmall women's bike with 26" wheels. I don't recommend that, as she tried out a *bunch* of bikes before we settled on that and it was a touch big for her at first, but I'm fairly confident that a 20" would be too small for him. I'd be more inclined to go with the MT200 for a 9 yo boy if I weren't sure.

We just got my 7yr old (49") a used Trek 220. It is a 24" wheel. It is a tad too big for him but it took him a day or so to get used to it. It will be good for him since he is growing like a weed.

Thanks for the help everyone. As much as I didn't want to drive, I took ebartom's advice and went to the LBS. My son loved the MT200, and as mentioned, the Jet 20 fit well but wouldn't last a year before he would need to move up.