Considering my age

I had a phone conversation yesterday and it's still bothering me.
I won't go into gory detail, but a nutritionist called me regarding blood tests I had coming up. She wanted me to remind my doctor to include a certain test, for blood fats or lipids, I think. Either that or she said limpets. I don't think there are blood limpets, though.
I did love Don Knotts in The Incredible Mr Limpet:

But I digress – wantonly, deliberately – because what she said, after I asked why they needed this particular test, made me want to beg her pardon:
"Well, considering your age, I think it's a good idea."
She used this phrase three times! I'm 39, for fuck's sake!

Since when did people in their thirties become subject to this polite condemnation?