DS1 is only 18 months so obviously DP or myself still bathe him.
I try to shower with DS1 as little as possible, only because I spend all day with him, and he co-sleeps so that's my alone time, but he almost always goes in with DP, and neither of them mind
If he does want to come in with me though, most of the time I let him.
I'm with everyone else, I guess it will stop whenever any of us are uncomfortable with it. Same for DS2 when he comes along