Is it normal for dad to take bath w 9 yr old son?

Ok..I know..but my bf son who's 9 year old son wants him to take a bath with him...my bf and his ex we're very, like nudists.. I think he'd too old..and its a bit strange.. also my bf has always spoiled his son...and its crazy..but he allows his 9son yr old son to not wear a seatbelt anymore.. I got mad and said he's being ridiculous..and he only makes him wear it when he has to meet his mom.. is any of this really wrong or what?? Thank you