Help with starting my 17 year old's first tax return. Do I use my personal Turbo Tax account or should he create his own?

If you start a separate account for your son, then he can take over the account when he starts doing his own tax returns. 

But if you are using a multi-return package, then you will need to prepare your son's return in the same account where you used the activation code, or you will end up paying for his return separately.