Well my tuppence worth is this…
Do it when you feel like it. I did about 6 months riding round central London when I was 17 on a derestricted KMX 125. ( 85 mph in Hyde Park no probs.) Then did my test which was one of the first of the normal persuit tests we are used to today.
I think you just know when you are ready and I moved on to a couple of years on a late FZ750. It was a huge jump up but I’ve never looked back. Everyone is different and I’d just follow the course that you feel comfortable with. Its all good!!
OOPs See…http://londonbikers.com/forums/shwmessage.aspx?ForumID=35&MessageID=71789