His favorite thing

Since he was a wee babe, has been anything with wheels.

 Okay, so I may have influenced him a bit...

 But really, he's only ever shown real interest in things that have wheels.

 Other than mud.  Mud is his second favorite thing, and you can combine mud with wheels, and that's just the best ever.

 I don't think he's gender predisposed, I think he's genetically predisposed to loving things that go.

 I mean, his father and grandfather both have a "thing" for oil, metal and tires.

 And why shouldn't he love them?  After all, this stuff is lots fun.

 I've come to the conclusion that had he been born before the invention of the wheel, he's the guy that would have figured it out.

Just from the simple, desparate need to have something that goes.