When I was a yoof, a BMX with a layback seatpost (very laid back) was amazing for wheelies. It was difficult to keep the front wheel on the ground when sat down, with your weight right over the back wheel. Modern BMXes are much harder, generally having straight post, usually with the seat dropped right down. Therefore a terrible choice for an off-road ride of any distance.
My 14 year old gets on fine wheelieing a 26er xc hardtail mtb (2nd hand sunn travis frame bought for £50 and built up with spare parts), but he’s reasonably tall. Would be perfect for school run and extended off-road rides, right through to adulthood.