It's not just people offering seats, it's the other examples of bad manners.
The other day, I went to catch a train into Glasgow. The carriage door next to me wouldn't open and as I moved up the platform to get on the train, I was pushed out of the way by the many young people who were standing on the platform. Not as much as an "Excuse me", from any of them.
Later on, I was waiting for a lift in a dept store, when a young mother came up with her partner. When the lift arrived, she and her partner barged in front of me and positioned the pram, so that it was difficult for myself and another lady to get in, despite the fact that we had been there before her.
It doesn't matter whether you are young or elderly, good manners cost nothing.
It could all be due to the fact that I am so small, I am invisible.