[pitdogrider]

Legally no you can't have a standard KX125 on the road on a CBT. CBT allows a 17yr old and above to ride a bike upto 125cc with a maximuim power output of 11kw.
KX125 has around 33hp (24kw), year dependant. Meaning to legally ride one it would have to be restricted and a certificate provided from a reputable garage but if you wanted to just buy one already registered there'd be nothing stopping you taxing and insuring it and dealing with the consiquences when something happens.... and that's if you get to use it much in between its monthly top end rebuilds and quarterly bottom end rebuilds. It's a great idea but there's loads of downsides.