I am nearly 40 and can only give you my very dated experience.
I had in excess of 20 (yes, 20!) grommet ops between the age of 2 and 12.
At 12 my mum decided that I would have no further surgeries.
I prob had my last really good infection at 13.
I have been pretty much fine since, although my sinus situation is pretty dismal.
Be careful with the fess sprays, I find that prolonged use gives temporary relief, but longer term is a bit of an irritant.
Maybe give him a bit longer to grow out of it?
Beach swimming had always worked for me too. Cleans everything out.


ETA, my hearing is ****e... I am fully expecting to need a hearing aid by the time I am 70.