Where to start racing with GT Cars?

Hello, first post here. I'm wondering that how can I start racing? I have been doing karting for couple of years in national karting series, I am 24 years old, is age is as important as open wheel series for GT series or not? Is GT4 is good to start or should I start from lower spec. cars? Earning money from GT series possible ( at least the money I spend to race) ? I am looking for roadmap. Need some advices.