I'm looking at your proposed names. I think it's good to be more targeted, so the age works better than just 'aging'. And I think @over60health is more visually attractive than @over55health. It even reads better, rolls off the tongue better. Also, people tend to think in decades. 20s, 30s,40s,50s,etc. Your original idea might be best. A 55-year-old would surely look at such a blog. 60 is looming. I think anyone who is 55 has an acute sense of aging. The 55/56-year-old is already losing contemporaries to premature heart attack and other diseases. My son is in his early 50s (oh, no I didn't say that...it kills me). He is suddenly struck by the reality of his own mortality.

I think @over60health suggests the blog has something to say for a particular set of individuals. The idea caught my attention immediately. I would expect to find useful information on such a blog. I might give it a try and if I found the material to be vacuous I'd never go back :))

I'm no good at marketing or appealing to people, so take my opinion with a grain of salt.

Whatever you do, I'm impressed🌹