I got my account a few years ago because of that "Under 13" thing, can I change the e-mail to my e-mail?
Yes if you log in to your account you should see a row on the left side with:
'Your user name'
'Pokémon TCG online settings'
'Play! Pokémon settings'
If you click the 'profile overview' tag you should get a new page with all your profile info. Underneath 'user name' there will be a box with your current e-mailadress. You can delete what is written there and typ your new e-mail adress. Then click the 'save' button on the bottom of the page.
Hope this helps.