friendly debate. When are boys to old

Hmmm....I never really though about it.  I guess it's on a case by case situation, considering age of child, bathroom location, etc.

I understand that. Rest stop can be very dangerous.

Quoting Summerlion1123:

My son has gone in on his own with me standing right outside since he was about 5 or so but even now (he's 7) if I feel uncomfortable I'll take him into the women's with me. We just went on a long driving trip to see family and at the rest stops I usually took him in with me.

Age 4 is too old, in my opinion. 

7.

My son stopped and just refused to go inside the women's restroom at 5. I had to wait outside the men's room for him.

My son is 5, and I still take him to use the women's bathroom.  I don't know when I'll start letting him go to the Mens room alone.  

 I use a family restroom until I feel comfortable. It really depends on where I am.

my son is 5.5 and he will be coming with me for a long time. between his spd and his anxiety I'm just happy he will now go in a stall alone but only if I'm holding the door or in the stall next to his.

It depends on where we are. I started letting my son go alone around age 5 in washrooms without stalls (just a room with one toilet), or places that are not busy.

My son has become very aware of there being a boys bathroom and a girls bathroom.  As long as there aren't too many people in the men's bathroom or we aren't in a busy place in general, I'll let him go in by himself.  He's 4.5