If someone is 10 years older than you would it annoy you if they

If we weren’t on joking terms yes, I’d find it patronising.

Someone 10 years younger calling me kiddo would be so much worse

I get called kiddo by some of my co-workers. Thing is I'm 34 and they're in their 30s as well. I really don't mind it. XD

Yes calling me kiddo would annoy me, I'm 39 years, I'm not a kid, even though I didn't pay attention the last time my housemate called me kid.

I guess it would depend on the tone the person said it in.

If I feel like they are only saying it in a well meaning "I'm only saying this because you are younger than me with no intention of being annoying".

Or using it as a part of the regular dialogue of where the come from like how some people call others sugar and stuff than no I'd have no problem with it.

i'd find it endearing

it would annoy me no matter who called me kiddo

Depends on the person, whether we were friends or not, and how old they looked in comparison. Mostly the friend part. If we're not friends, it's always condescending.

I feel like it really depends on your own age rather than the age difference. If you're younger than 30 I think it's normal, but if you're older it can only sound condescending.