A preteen a kid should play with his friends in whatever the age range he's in. At thirteen and in 7th grade a kid belongs on a 60/90 field. He has two years to prepare before high school. A 7th grader should not be playing on a LL or 50/70 field.
For most kids 60/90 at 13u is acclimation to the field size change. At 14u the game speeds up significantly. The following year the kid shoud play talent specific rather than grade specific from that point on.
Playing in age ranges used to be normal. I played LL from 9-12. There wasn't majors and minors. There were five players in three age groups. If a kid was good enough at nine he counted as a ten. Then Babe Ruth ball was the same thing from 13-15. All players were competent. No one was handed a uniform. Everyone had to make it. There were other leagues for the leftovers. Then Legion was the best fifteen 16-18yos regardless of age.
In this era we weren't stars every year. We had to compete to work our way up the ladder. I was terrified of 12yos when I was nine. At ten I was at least lying to myself convincing myself I could handle it. Being 13yo in Babe Ruth was a challenge too.
The other thing is pitchers weren't smoking their arms every year. I didn't pitch at all until I was eleven. I didn't pitch at thirteen. I only pitched a little at sixteen. I'm guessing a 13u or 14u pitcher has more mileage on his arm now than I had entering college ball.