My MIL, seriously, she is 70 and always looks amazing.
I have know her since i was a child (our parents go way back) and I remember as a child thinking how well put together she is/was IYSWIM
I think for her it is that she wears a bit of make up, not much mind, always has her hair done, sometimes she has it done at hairdressers sometimes herself (i'll never forget the time i came around to hers un-anounced and her hair had curlers in it, i did get a telling off!)
Clothing wise she has always gone for high end brands, not obvious ones, think Lakeland etc, and she looks after them and they have lasted.
She picks classic clothing, similar to what someone else said, eg a lovely shirt with a blazer and nice pants - not jeans, or a twin set.
She also wears pearls - always, i love them too.
She is about 5ft5 and i would say a size 14.
I really do admire her.