I realize that older developers are slightly uncommon, but maybe it's also because they get bored and think they have better career prospects elsewhere. Personnally, I still love to code and learn new things, as I've always had. I'm used to working with people younger/older than me and it has never been an issue either.
That being said, I'm anxious that age becomes an issue along the road. There's also no denying that there is some sort of discrimination against older people. Simply look at the pictures on companies websites and presentation material, they clearly want to show how diverse they are except for older persons...
I'm just curious: older people working in big companies, have you ever discussed that with people in charge of promoting/ensuring diversity? I think there's a good point to make.