I no longer work for nats, but while i was there I hadn't heard of a gap year (Could have changed). But I did spent a just over a year working as an assisstant with Nats before the ATC college. I found it very useful, and would recommend trying it if you unsure of your options.
The thing you have to be aware of is that, it doe's take a while to get throough the ATCO selection process, and I wish i had started in ATC at you age.
Good luck in what ever you decide to do.
P.s I don't know if they are still recruiting ATSA's, but have a go.