I think that you misunderstand the reason for the 
law.  It was enacted for the express reason to 
protect kids under 18.  True, it is persumed that 
those under 18 can't make rational decisions on 
their own, but they should be greatful that adults 
think that way, because it allows kids to make 
mistakes without being held completly responsible 
for them.  That's why legal contracts, like on Ebay 
are not bidning for them.