Your problem will not get better as your son gets older.  My older son has 
about 18 years on yours; however, he will use any excuse/story/lie to get 
to drive the old man's "Luv Bus." Even though he has his own 72 Super 
Beetle, MY bus is his vehicle of choice.  What you will come to value is 
his help in working on one or all of your vehicles.  Call it male bonding 
or whatever politically incorrect phrase you desire, there is something to be 
said for having both of your kids (be they sons or daughters) help you swap 
an engine or replace a broken clutch cable.

Peace,
Skip Correll
Chattanooga, Tn