Can anyone give me some advice on if a boy school or a mixed school better for a boy who's not so boyish? Thanks a lot.

What do you mean by 'not so boyish'?

not too rough, a bit sensitive and a bit more reserved

What choice do you have where you live? I chose a mixed school for my DS but not everywhere in Bucks is in the catchment of more than one GS.

My personal view is that mixed education is better preparation for working life and life in general than single-sex education. I accept that there are some children at some points in their lives that might be better served in a single-sex environment, but five to seven years by choice is overdoing it in my view. If I had the choice, I would go for co-education.

I live in Milton Keynes. So we have Royal Latin School and Aylesbury Grammar School nearby.

Have you checked recent years' allocation distances for AGS and RLS? I know that the southernmost parts of MK have previously been in range but distances are reducing generally. Parts of MK are very marginal for both schools so the distance may override your preference anyway.

How close though? There's also Sir Henry Floyd in Aylesbury but you aren't in catchment for any Bucks GS I think.

we may think of moving to a catchment area later on, but we can't decide if we want our son to go to boy school or a mixed school, which obviously determines where we are going to move...

You have the choice in Aylesbury ....