@Meruem
There seems to be an obsession lately of not wanting to accept older ages. Of course 70 is elderly. The same way someone in their 40’s is not “young”. I don’t get why people find that so hard to take. I’m in my early 50s and so I don’t see it as some kind of insult if someone calls me middle aged, it’s what I am. I might feel younger in my mind but my age is what it is. No matter how fit I am or how I feel or look. They’re just descriptive words that people seem to take as insults.
This ^ in spades.
I don't understand why ANYone is so offended that someone of 70 (in fact, over 65,) is called 'elderly.' They ARE elderly. As you said, it's not an insult, it's just a description of the age group.
And just because someone doesn't feel elderly, and runs a marathon a month, plays squash, and works 50 hours a week at 73, that doesn't mean they're not elderly. They are still elderly.
As you say, why are people so offended by it?
Comments like 'my 73 y.o. mother/nan would kill you if you called her elderly' are bizarre. WHY? Why would she 'kill you?' She IS elderly. 
Also, like I said a few minutes ago, I don't understand why 'not looking your age,' is celebrated so greatly. What on earth is wrong with looking your age? And as I said, virtually everyone looks their age within 5 years in either direction. Yet, some people seem DESPERATE to be thought of as looking much younger... and insist people think they are their daughter's sister, and claim that they are asked for I.D. to buy booze even though they're 43! Bizarre! 