How offensive are the terms eternal bachelor and spinster?

We have a male and female colleague, both of whom are in their 60s, neither ever married and both lived with their respective parents right up until their parents passed away which was fairly recently for both of them.

During a chat at lunch today where there were around 10 of us present including these two people. One of my colleagues referred to them as an eternal bachelor and a spinster.

It wasn't said in a malicious way (I think) and they didn't respond angrily, but I couldn't help thinking that these are quite offensive terms these days. The person who said it was mid 60s too, so maybe it was not deemed offensive previously.

Interested on others thoughts.