At 12 even parents do not always know what he craves.
The OP may think that giving cash means not exciting enough without a gift to unwrap, BUT if really interested in what is the best brithday pressie, then cash is the answer.
You can purchase cash cards. Sort of wallet type thing you can put whatever amount in notes you wish to give, and then wrap this up. Gives a pressie to open and can also add some chocolate.
I only purchase birthday and christmas presents for my g.children up to the time they leave Primary school - from then onwards it is always cash. Sometimes, they use it immediately - and I do not care on what -their choice. Sometimes, they maybe saving for something big.
At least I know I am giving them what THEY want to receive, - not what I want to give.