Bat Length

DD is a pretty big strong kid (13 next March; 5'7" 135 lbs) who swings a Demarini CF8 33" drop 11. She takes private lessons plus hits 500-ish balls per week off a tee into a net in the garage.

I'm wanting her to get a heavier bat because I think she's plenty strong enough to swing it so was planning on making a relatively minor move to a 33" drop 10; maybe an end-load. She could probably handle a drop 9. I asked one of her coaches (who hasn't seen her swing it yet; the team was formed this fall so not all of the coaches and players have been at the same place at the same time yet) about bat sizing and one of his first comments was "33 inches is probably too long for a player that age." I'm not sure I understand how whatever makes a bat "too long" for a player is age-dependent. I think most of the girls on the team swing 32/22 but she towers over most of them.

I've looked at all the bat sizing charts I can find but am wanting some practical advice on bat selection. Thanks!

Bat size is largely about player size and strength, and not so much about age. At 5'-7", 33" is not too long (IMO). Also, I would look to move her into a -10, for sure - especially if she's reasonably strong. An end-loaded bat isn't out of the question, either, but that's more of a feel preference thing.

For comparison, my kid is 12yo, nearing 5'-4", and 120-ish lbs. She's swinging a 32/22, and we are expecting to move to a 33/23 soon.

My 12 Yr old DD made the switch after fall season was over. Went from a 33" drop 11 to a 33" drop 9. Her hitting coach suggested the move. Never looked back IMO if DD is strong enough and has good technique there isn't a fits all chart.