It would almost certainly follow an approximate normal distribution just like the above graph. Why would it look different?

Average is the mean, not median or mode. This doesn’t change on context. Average is always mean.

I’ve raced motocross and also raced woods events and also do a lot of other off road riding on quads and UTVs. As the guy before me said, CC size isn’t always going to directly reflect power. A crf450L has a 450 race bike engine and has much much more power than say a DRZ 400. I would suggest going with a CRF 300L. It will have enough power to handle almost all trails outside of steep steep inclines. It’s a great bike and doesn’t require much maintenance and is relatively inexpensive. Also couldn’t go wrong with the DRZ 400 but I think it might be a little heavier and slightly less capable. When riding off road, too much power is often a hindrance rather than help. You can often go faster in the woods on a 250 race bike compared to a 450 because it is lighter and you are not having to fight the power output of the bike as much. A 250 4-stroke or 125 2-stroke bike would be a good option for starting as well, but they aren’t typically set up for registering for road riding.

Good luck if you decide to get a bike. Take it slow at first, off road riding is much harder than road riding and there are a lot of lessons to learn that are best not learned the hard way. ATGATT