Welcome to the world of internet chatter, where no one would ever lie or exaggerate about their son's sports abilities in order to make themselves feel superior...
Some time ago an orthopaedic doctor, Dr. Michael J. Axe, compiled an actuarial table of expected throwing velocities for 8 - 14 yos. Here are the average velocities:
8 yo: 40 mph
9 yo: 43 mph
10 yo: 46 mph
11 yo: 48 mph
12 yo: 50 mph
13 yo: 54 mph
14 yo: 60 mph
Dr. Axe also provides numbers for 1, 2, 3, 4, and even 5 standard deviations above the averages for each age group. (If you're not sure what std. dev. refers to, think of it this way: A thrower who is 4 std. devs above the average velocity for his age group is a 1 in 100,000 level thrower. 5 std devs is a 1 in a million level thrower...
Here are the "1 in 100,000-level" velocities:
8 yo: 54 mph
9 yo: 59 mph
10 yo: 62 mph
11 yo: 64 mph
12 yo: 70 mph
13 yo: 74 mph
14 yo: 84 mph.
However, if you read the irresponsible b.s. posted by some people, you could only conclude that everybody but your child is far above average. This is really destructive stuff.
You should not be pushing an 8 yo child (or a 12 yo, for that matter) to achieve the highest possible velocity in his throws or pitches. Instead, you should play lots of low-stress catch with him and learn enough about pitching mechanics to guide him into a mechanically efficient delivery.
Expect that his delivery mechanics may change considerably over the years as he grows and then passes into puberty....steady practice and repetition of pitching skills over those years will help him much, much more than any advice like "throw harder, kid, you are below average according to what anonymous people are saying about their sons on the internet".
There are some outstanding coaches at LTP who can help you understand this stuff better than I can, if you stick with it...