When should I start covering up around my son?

My son is 6 going on 7 and my mum says I need to stop being naked in front of him so often (every day) stop showering with him (he sometimes joins me in the shower, on his own free will) it's always been just me and him and I know there's nothing sexual about it at all but I know that I will need to stop soon. What's a good indication that I should stop?