I had a 50cc in Guernsey when i was 14 beacuse you can have 50cc's at 14 over here, it was 300 fully comp.
What ever you do dont buy a performance exhaust they sound gay.
Out of a rs you should get bout 55-60 flat out if you have a long road and a tail wind.
Have fun with yout 50, dont be too dissapointed when it doesnt, really go that fast!