I've seen fifty year olds that seem eighty and eighty year olds that seem fifty. We're all seniors after fifty five. I think you're elderly when you need permanent help in day to day life.
I always cringe when a news report calls a person of seventy an "elderly victim". Especially if that " victim" kicked the crap out of the youthful perp.
I turned 90 last winter and my worry is not seeming to be fifty, but if I slip by that middle age number and end up more like I'm five That's when folks know I'm really in trouble, although I probably will have a closer relationship with my great grandchildren.