I always do at least one golden age right at the beginning of renaissance era. I find I often start to lag around this time because the beaker cost of techs spikes and I like to get universities up in 6 cities to start working on oxford. So i usually pop the artist i get from Music, and one other. This really gets the ball rolling on techs like education, printing press, liberalism, nationalism, etc. which have nearly double the cost of most medieval era tech. At the same time, use the increased production to get a big head start on universities. Usually I get liberalism around this time, which can fit nicely with nationalism -> taj mahal for a second golden age.
Late in the game the only GPs I use are engineers and artists. No more shrines to build, extra academies don't make much difference (usually less than 1% of the total tech cost) and the beaker bonus for direct discovery is relatively negligible (usually less than 25% of the tech). If I have a prophet, merchant and scientist available (e.g. from physics, economics, + extra prophet), I'll do a late-game GA, usually during a space-race push, culture-push or military buildup.