My 13u team (I organized it and coached) was a group of players who were the best all stars in our eighteen league LL district. I didn't look for the biggest kids. I looked for kids most likely to develop into high school players. Our coaching goal was to get them there.
There weren't any throwing issues. Every kid had a gun relative to their age. I was prepared to tell catchers one hop it on a line to second versus heaving a rainbow. But it wasn't an issue. About half the team had not played with leads. It only took a weekend of games to get comfortable with leads. We spent an entire practice on getting way off the base and learning where "too far" was. From a fielding standpoint the only issue was learning how far to run and it's still your ball.
On the 60/90 slow kids get exposed. The kids who hit the moonshot homers got exposed. Slow runners were thrown out with the long run to first. Or they were held to singles on what should have been doubles. Moonshots on smaller fields were now catchable fly balls. I do remember 13u as being slow motion baseball. It gave the kids reaction time. The game sped up significantly with 14u.
My son was 5'2" in 13u. He threw 68 in LL. I wasn't worried about throwing for distance. His line drive homers in LL became doubles and triples on the 60/90.
i do remember his first 13u game in the fall after LL. in his first at bat he ripped a line drive shot on one hop to the second baseman for an easy 4-6-3 double play. He returned to the bench bitching he can't hit the ball any harder. It probably would have been a gapper to the fence on a small field. The next time up he crushed one to right for a sliding triple where he just beat the throw. He looked up at our 3rd base coach and asked, "Was that out of LL?" The coach replied, "Son, you're done with LL."
Re: out of LL ... We had a very loose bunch in Legion ball. We were always riding each other. If we were winning and one of our hitters flied out routinely he was sure to hear, "Nice try. That was definitely out of LL."