When they start becoming uncomfortable or asking for privacy themselves.
I don’t feel like you can put an age on it.. one day they will just stop coming in when they know you are changing because they don’t want to see you naked anymore 🤷🏻♀️ probably pre teen age of around 9/10..
He’s 5 and I haven’t stopped
My son’s 3 and he used to ask A LOT of questions. He doesn’t tend to follow me anymore but if he’s in the room I’ll still change infront of him then he will say “that’s your boobies” then tell me why I have boobs and why he doesn’t, or in the bathroom “I see your vagina. You’re a girl, I don’t have a vagina, I’m a boy” then carries on with what he’s doing. He will do this in public toilets aswell 🙄 I think I will let him decide when to stop following me and coming in on me changing. It is getting less so I guess it’s already started. In my head I’d say 7/8 I think id stop it myself but not sure until I’m there. But definitely before puberty