Hi OP, I have a 12 year old DD (Y7) who trains similar amount to your son. She's no where near as good but loves her swimming, we often lose the will to live sitting poolside gala after gala, so I can empathise with you!
My personal opinion is if he loves it and you are prepared to keep supporting him to develop, move him now, not at Y7. DD started senior and new club (very competitive one) in Sept, and it takes a big adjustment, given the extra homework, commute, school etc etc. Mine currently does 10 hours on top of other stuff like music, hockey etc. This is not the top rank squad but one we negotiated, given her other interests (and not at regional level). But she has to keep up the sessions of 4/5 x or lose her place.
Advise from chalet is spot on, as many children do develop later, and we are watching carefully the tiredness/homework on time factor. Having made the move, she's starting to benefit from the club's training, but is not a natural like your son. Body changes will also effect form (and impact on motivation) and we are hitting that now as she is playing catch up on ability vs her new peers.
However, one if the biggest benefits is the wider friendship groups formed. May not be a consideration for you now, but her extra curricular stuff always gives her more genuine, longer term friendships than school alone, and being on the swim circuit for a while has created a camaraderie (boys and girls, across all local clubs) that we really value, especially given today's challenging social media world that children have to navigate in!
Yes, it's tiring, but the longer I can keep her away from the small screen and socialise amongst real kids (whilst keeping fit with a healthy body self-image), the better. Not once has a boy commented on her appearance at the pool, unlike at school. I know which ones I'd rather she hangs out with...who will hopefully continue to be the gents they are now!