CMcMahon makes a valid point. My knee-jerk reaction could've been ' why a 20" wheeled BMX'
A 30yr.old nephew of mine has a few bikes at his diposal. At 210 he's in superb shape, he's a Phys-Ed teacher and likes his BMX bikes alot. He rides 'em all over town. I think it's funny, he doesn't, you don't either.
Mongoose has a site. DiamondBack comes to mind but .... there are others as well. This brand & others can be found at not so pricey LBSs. A sporting goods store named "Dick's" for instance as well as Ski/Bike stores... other all-around stores have good bike depts. Knee-hitting size never came into play with my nephew; the sites/ stores can guide you.