A tough one I know. We have 8 children between us and as they were growing up most of the boys showed an interest in motor biking. We didn't encourage it and they moved onto cars (3 of which were written off in their first few weeks of driving). However our youngest daughter asked for a CBT course for her 17th birthday. We didn't argue with her or try put her off, we just ignored her at first hoping it would go away, but it didn't. So we booked her into the Harley Davidson riding school at Builth Wells on the basis that we could at least give her the best possible start. After the course she then of course wanted a bike. So shortly afterwards a chineses 125 cruiser joined the fleet. She rode it nearly every day for about 9 months through all weathers commuting to 6th form through very heavy traffic on the A6. There were a couple of incidents, but not serious and I'm sure she benefited from them. She went back to Rider's Edge at Builth Wells for a 6 day course ending with taking her test on her 18th birthday, which she passed. She had the bike with her at university on her first term last autumn, but has left it at home this term since she didnt' think she'd use it much thru the winter.
I still wouldn't be as keen to help any of the more impetuous boys at the same age, but our daughter has made a very good and competent rider and at the moment she is not on a very powerful machine. I feel we gave her the best start we could, she is sensible and I think the risks to her on the road could be just as great if she were riding a push bike.
Would I encourage it - no. but we did everything we could to help her be as safe as possible.

__________________
If you think you are too small to make a difference you have never spent the night with a mosquito.