TCockman, welcome.
You're going to get several responses telling you not to worry about velocity at such a young age. At 10 years old, building sound mechanics are vastly more important than velo. Don't sweat the fastball...yet.
Having said that, I was one of the nutjobs who had a gun on his kid at 9 years old. (I would tell people that I was only looking to gauge changeup differential, but they knew better). I wish we had spent less time throwing to that damn gun and more time working on mechanics.
Now, to your question...we're several years removed from the 10-11 days, but I would guess that 55 MPH or so would be average for an 11 year old, with the harder throwers touching 60+. At 12, maybe 60 MPH average and 65+ for the elite. I'm guessing, and these number will vary wildly based on what part of the country you survey.