"maybe not 'young' but in no means old!"
If only we had a word for that, oh yes, middle age.
"55-70 is middle-aged" Almost 40% of people don't reach old age by this definition. Saga, Age Concern, etc need telling, as they have it very wrong.
Put simply: first third of life (0-30) is young, second third (30-60) is middle age and the final third (60-90) is old. Of course most people don't reach 90, but its a pretty good approximation (pitiless yank gives the traditional definition, but life expectancy is increasing).
If your self esteem is tied to not labelling yourself middle aged and imagining 30s is still youth, then the issue is with you, not the English language.
P.S. Yes, I'm middle aged.