Jump/Stunt bikes come in a variety of types and styles. My step brother had one that had 6 gear cassette on the back and single front. Looks like a cross between a mountain bike and a BMX and the saddle post is "normalish" height.
Best bet is take him to a bike shop and let him have a look round, if its decent you might get a sales person to have a chat about the different bikes with him.
They do. The one I linked to is a Scott Voltage, normal saddle heights are part of its repertoire. Giant, Specialized etc. all do them in their range and they all look pretty cool whilst at the same time being fairly capable bikes.