I honestly started watching yaoi anime at 12, started reading yaoi at 14. I'm 21 and I still read yaoi (now yaoi manga) but haven't found any yaoi anime that I haven't already seen.
Though honestly I think you should at least be 20 before going into yaoi. I only say this because at 12 I got in big trouble when I was caught watching a Yu-Gi-Oh fan-a......
