I learnt to ride on my dads 1985 GSXR750 when i was 15. Then when i got my licence, i bought my first bike a Kawasaki GPX250, it may look ugly but it was hell good on fuel! Then i bought a Kawasaki ZXR250, its better then a CBR250RR. Looks bigger, handles better, upside down forks etc. Then i got a 1988 Suzuki GSXR750 Slingshot (still got it). Then i bought my Suzuki GSXR1300 Hayabusa!
Start with a 250cc bike cant go wrong. I have mates that dont have a bike licence but ride like a ZXR600 and a GSXR1000, and they are scared to turn! Master your 250, then move on to a bigger bike if your confident enough.
Ride to your potential and not the bikes!