Here's my .02, my youngest was a 13 last year, & again very dominant for his age. Back before the national age change, he played on the same team with several same grade, but much later birthdays; ie, May & June's of the following year. This was very commonplace. After the age change, nearly all of the dominant local AAA-Major players of my youngest son's age were all the "old" ones with birthdays from May through September.
After the age change on a few occasions, both of these younger ballplayers played up a year in a tournament or two on the same team with my boy. All are solid Majors players & have been in their age since the 10's. Both of the younger ones could get the job done immediately when they jumped from their normal 50-70 fields to the 13U 54-80 fields.
Today, both of these 8th graders are 5-2 to 5-4 & I'd bet neither weighs more than 115lbs. I'm sure they will end up playing against some absolute "man-childs" this season. One could say, these 2 are small for their age, yet with the height of their parents & grandparents, I'd bet they will be well over 6 foot when fully grown. On their respective 13Majors teams both can play any position, & I'm sure neither would have little problem playing on "the big field" this Spring... too many tools. 60-90 won't be happening for either this Spring, as both of them will be repeating 8th grade next Fall. In our state they can only play 8th grade school ball once. Another year to grow & fill out can't hurt them at all. Bigger, stronger, quicker, & another full season of Majors travelball, I'm sure ending again after Steamboat or Disney, that can't hurt them, just Mom & Dad's pocketbook
Over the years, I've witnessed a bunch of local "younger" ballplayers repeat 8th grade. Quite a few others repeated 5th grade for similar reasons. For all means, check out what your school district's policy is. Know of several local districts that won't allow repeating 8th grade, unless the student is just dumber than a post. That doesn't help. Good luck in your decision.