Since I didn't want to go back and edit my post on manners, I do want to say that these findings are for caucasian men. Ethnic groups vastly differ:

Indian men will never hold a door or say "thank you" if I hold the door. I could be naked, the door will slam in my face.

Arabic men will go through a door I am holding and will always say "thank you". They always offer to take the door first..at any age. Doesn't matter what I'm wearing and usually the most friendly of any group.

Koreans, Phillipinos, Chinese etc, will hold the door open at any age - men and women. They always speak, never initiate any conversation. They have a tendency to look visibly uncomfortable to have someone hold a door open for them.

Black men of any age will hold the door open, acknowledge a "thank you" and will always say "thank you" for a door held open. Black men over 50 will usually not go in first but will insist they take the door. Clothes doesn't seem to be a factor here either.