Today, I sat in a reserved seat when I didn't see any seniors, disabled, or anyone else in need around me. As I sat down, a dressy woman who appeared to be no where near senior status said to me, "I'm a senior citizen, I need to sit." I wasn't going to question her claim. Besides, she was older than me, that I much I know. I complied and said, "Sure, of course." A few stations later, I found myself seated in another reserved seat. An older man walked in. He had head full of silver hair but his face and physique appeared to be much younger than 60+. After the incident with the woman, I wanted to volunteer my seat but didn't want to insult him either in case he was just prematurely gray. I watched him for any signs of wanting a seat. I just couldn't tell. Well, I ended up sitting the rest of the way and he ended up standing while reading a book.
With females and children, it is much easier. I can immediately offer the seat and they'd gladly take it. With some men, it can be offensive. I've seen an old gentleman who got irritated when everyone kept on asking him if he'd like to sit down. He ended saying, "No, I am old but I can stand on my own."