Going through the replies I see that most of the posts so far are about older people or people needing (or not needing) extra help etc.
Maybe my story is a bit out of topic because it doesn't fall in any of these categories but anyway, I'm saying it as I find it quite interesting.
I did my OW cert dives together with a young (around maybe 20yo maybe even younger) lady (among other people). She was perfectly healthy and physically able to handle everything herself.
During the first (shore) dives I noticed the instructor helping (i.e. doing it for her) donning and strapping her fins.
Next day we were preparing for a boat dive. She was seated just across myself on the boat and the instructor was busy doing other stuff at the back. After I got ready (weights, BCD/tank, fins etc all on) I noticed that she had her BCD/tank,weight etc on, but fins on the floor and she was looking at me, then her fins, back to me and all over again for few times. The message was clear. My reply was even clearer - I pretended I don't see/understand anything.
After a while she got the message - her face became quite upset as she was bending trying putting her own fins on herself. With some frustration and effort (as it was probably the first time ever she did it herself) she managed it fine.
I usually do help people, quite often I offer help even before I am asked when I see people struggle, but in that case I felt that if somebody is not even willing to try put his/her own fins on, diving is not for him/her. It was not about her abilities. It was about her mentality.
@stephen. How is it that you know she is "perfectly healthy and physically able to handle everything herself?" Many physical and other issues are not overtly obvious to others, but are very apparent to the afflicted. Arthritis is a prime example. As one who has five artificial joints, I can assure you that on most days I have no issues, so no one but the crew is aware I might need help. However, every now and then, one of those joints gets inflamed and joint mobility/range of motion can become problematic, and I need to ask for help. Hopefully a crew member is not busy if I need an assist, but if that I not the case, I will ask another diver, usually the one sitting next to me. It is a lot easier to ask for help when needed than give up something I love to do because of an occasional problem.
Edit: Bottom line--you likely are not going to know what physical problems others are dealing with, but when you become aware, be a nice person and offer to help.