There are no reputable stats on the average age of death of “gay” men or women. Any age reported is like picking a number out of a hat. Why? Deaths are not reported as “gay” or “straight”.
Check out the publications within this community to get a glimpse. Before they took it down, Dallas's "gay" chorus Turtle Creek Chorale had a "member memorial" webpage where members who had passed on could be posted, and members who knew them could post info about them. It was very revealing. These were well-to-do, affluent men (it was a very expensive proposition to be in that choral group) in an affluent city so poverty or "lack of healthcare" wasn't the usual scapegoat. Ages at death in the 30's, 40's and occasionally 50's were the norm, not the exception. Posters who were the most honest would admit to the cause of death being AIDS or some related infection, others would just say that the member "died quietly at home." Forty-year-olds dying quietly at home is far from normal.