Most of the older people in my family have pensions and social security, so there's no need for anyone to take care of them. They're generally in good health too. I think that older people who have the health and resources to sustain themselves would never even want to move in with their children.

I've also known childless eldery people, both straight and gay, who have had active lives with their friends, nieces and nephews, siblings, other relatives, etc. Just because an older person doesn't have kids won't necessarily mean that they are unhappy.