Domestic rats don't have different breeds. All domestic rats are just domestic rats or "fancy" rats. They may have different coat colors or ear placement but they're all Norway rats (species name).
As for your rat's age, you could look up "rat development" web pages to see if the pictures help. After 12-16 weeks, it's pretty difficult to determine age. If your rat is healthy, you could weigh it and look up weight charts to see roughly how old they might be.
To determine your rat's sex, it's usually pretty easy to tell because boy rats have giant testicles. If you're still unsure, google "sexing rats" to find a website with pictures or videos to help you.