How Old Is Too Old?

My question is this: How old is too old when it comes to my son being in the same room as me while I dress? Today as I was getting out of the shower my 4 year old announces that I have a "giggle bottom", thank you son, that is good for the ol' self esteem. Then as I am putting on my bra (I am a clasp in front then turn it around kind of girl) he tells me that I am putting it on wrong. I questioned him and he told me that the triangles go over those, pointing at my boobs. At what point is he going to remember this and need therapy into his 30s??