Hey, just wondering if there is ANY insurance companies in Ontario that will insure a rider under 21 and has one at-fault accident but no charges...

Not sure where you are in Ontario, I'm in the horseshoe and there are several "forgiving" insurance companies.  If you email the CMA (you can get their info from their site) they have a laundry list of 'Bike Friendly' Insurance companies and independant brokers, you should be able to find one there;

http://www.canmocycle.ca/

Good luck!

Hey thanks for the help man!
Lots of help 

Np.  In case they are slow getting back to you (or want you to be a member or something) I found all my CMA stuff so I listed some here for you to try;

Pioneer Insurance - Ask for Gord
(519) 744-4481
http://www.pionins.com/html/contactus/staff.asp

Insurance Central
(519) 756-3800

Hollingsworth Insurance - Ask for Rosie
(519) 742-5839
http://www.hollingsworthins.com/company.php

Dalton Timmis Insurance
(905) 633-9019

Tribute Insurance
(905) 681-6977

Wow man! 
Thanks for going out of your way to help me!
+rep

Might be worth asking on GTAM forums, since they are local to us.