Being old in and of itself is not a reason to criticize a person or pick a fight, especially a fellow fan.
A person, while quite literally a blue hair should not be treated as a "blue hair" b/c of age. The reality is that some older folks while able to get to the game do not have the physical ability to stand for 3.5 hours, or to participate in the stand/sit cycle a game becomes. Understand that the physical limitation of old age prevent some from standing or screaming as much as younger fans.
They've paid for a "seat" and have the right to sit, you have paid for a "seat" and are choosing to stand. By no means am I saying "Hey down in front!" but please try and be courteous. If there is an old person directly behind you and a space next to you, try and move over when you stand so you don't directly block somebody's view.
This does not excuse older fans who take it upon themselves to become ushers and regulate fan behavior in all matters, however they do have a right to object to someone blocking their view for an entire game. Both fans have a legitimate interest in watching the game and I understand the viewpoint of each, however, it is hard not to be sympathetic to the older fan considering the standing person can see the game while standing or sitting, yet by choosing to stand he blocks the game for others.
Generally, treatment of older fans where I sit is pretty spectacular. I go to the games with my dad, he is 80 years old. Manuevering his way through the row to get to our seats can be quite difficult for him yet most fans extend a hand and help him along. People in front of him sometimes stand up but he never tells them to sit down or shut up and because of this I think people are respectful of his rights in general. This works both ways.
Remember that these blue hairs were once students standing the entire game, they've earned the right to sit. As long as they are reasonable to you, please be reasonable in return. On the other hand if they are dicks about every little thing, all bets are off.