Unfortunately this whole situation arrises out of a very
simple matter of contract law. Below the age of 18 in the US, you 
can disavow any contract you have made as long as the item
is return in the condition in which this is sold to you. 
This includes the ability of any person under 18 to 
disavow any bids they have made without any legal reprecussions
against them. Since this is exactly what ebay must not and cannot
allow, the policy of 18 was set up. What you might want
to do is to go back to ebay and tell them that one of
your parents (or some other person over the age of 18 who
has significant tie to you) has co-signed with you ebay name 
and since they can be held contractually oblidged to any bid 
made, this should remove e-bays complaint against you and 
they should restore your account.

My 2 cents,
Marcus