What happens when you reach the golden age but you're not quite ready to accept the "golden age" moniker? Baby Boomers (anyone born between 1946 and 1964) might like to play golf and might choose to retire early. Yet, they flat out reject the term "senior citizen" with all of the implications that come with the phrase.
One report suggested the word "perennial" which means "lasting or existing for a long or apparently infinite time; enduring or continually recurring." That might be accurate, but it also sounds like a gardening term crossed over as a generational identifier.
Here are a few word and phrases to consider instead.
It sounds a bit like a steak (or the name of an indie science fiction movie), but the word "primer" isn't bad at least in terms of a positive description. Boomers are in their prime, ready to embrace their retirement years but not ready to stop working.
That report I mentioned already listed "elder" as one option, and it's not bad at least since we view anyone who is an elder as wise. The problem with saying elder is that it implies old and makes you think of someone on a church board or part of a college (or elderly).
One way to deal with the connotations of the phrase "senior citizen" is to directly confront the stereotype. Saying "vital years" lets anyone in a different age group that those around 65 have vital insight and ideas, not to be replaced by younger age groups.
Once you get past the association with the book series and movies, Twilighter is at least a description that fits what this age group will do--spend their twilight years starting a new career or working on new projects.
I like this one because it's what I plan to do when I reach this age. It's an opportunity to explore new ideas, to leave the old ways behind and embrace something new. It implies fresh energy and a new lease on life. It's also more of active verb, not a boring old noun.