Who's a Warlock vs a Wizard in HP?

[Amanda]

Well, I'm a Brit and I have always assumed JKR means to use the word to 
describe an old or elderly wizard. 

It is used both respectfully, as in the centuries old title: 'Chief Warlock of 
the Wizengamot' and less respectfully as in: ¡¥Madcap Magic for Wacky 
Warlocks¡¦ but both cases, and in the other examples you site, refer to a 
wizard who has reached a certain age. 

I really don't think it any more complicated than that.

Cheers, Mandy