Younger riders are higher risk because with little experience they think they're experts after a few months of riding.
www.sorrymate.com
58% of all accidents claims occur on 50-125cc motorcycles.
That's probably from commuting though.
I have also heard a stat that says the majority of fatal bike accidents are single vehicle but everyone blames other motorists for the most dangerous part of riding. At least here in the US, I will find the article and statistics.
I have not been able to find the article but i did find the stats from 2016. Ironically the article I read probably found a way to spin the facts to make it look like majority was single vehicle.Junctions is a big one in the uk