Cool, it is nice to see young people who want to tinker and lern god I am showing my age as above it will have to be a 50cc if you want to ride on your CBT at 16, but an engin is an engin, from when they first came out in ????? to now the basic principal has stayed the same, fule pumped in to a cilinder is set on fire that pushes the piston down and the next piston up! If you have got a year to play you have got time to find a knacker and do it up (obviosly look for one that isnt too bad) but YOU WILL DROP IT as with all lerning you will make mistakes so I personaly would start with a cheap bike and work from there as your experience and ability develop