You should hold the door open for the person behind you. That person appreciates it, and people who witness your act of kindness respect it. It literally takes a couple of seconds to perform a gesture that elevates you above the basic, selfish and inconsiderate. I believe that you are okay to do this for one person. Just one. Holding the door for 2 or more people makes you the unofficial doorman, or the weirdo with too much time on their hands. You should hold the door for everyone, but specially for the old and physically disabled.
If someone holds the door open for you, walk fast enough so they are not holding the door forever, and say “Thank you”. If you are too far away, gesture or say something to indicate that they should let the door close.
