People, we are talking about imaginary tickling a celebrity.
She happens to be 17 at the moment. Does it really matter which age she is if you just want to tickle her feet? This is not sex nor is it rape.
If there was an age limitation to tickle somebody, then most of use would go to jail for tickling our sisters or cousins. And they are possibly around our age. Oh my God, don't even get me started with that obnoxious uncle that every family seems to have that tickles to kids until they pee.
We need to make sure we maintain a clear perpective here. Unless you are looking at tickling as a preamble for sex, then keep it real. It is a fun harmless game.