This would be considered an adult model, so will have the wrist opening and finger stalls for an average adult hand size. This would be a great option for wanting something to last them awhile and that they can grow into if they have smaller than average hand sizes for a 13 year old.
The Nokona Bloodline Pro Series Baseball Catchers Mitt: P2 won't require a long break in period. There's not an exact way to predict when the glove is fully broken in. However, playing catch with the glove, using a modest amount of glove conditioner, and a mallet when needed can assist you in breaking in the glove.
The only way one would be able to get a catcher's mitt like the 2016 Nokona Bloodline Pro Series Baseball Catchers Mitt: P2 broken in would be to order a "used" option in "good" condition. These used gloves in this type of condition will more than likely be completely broken in. As far as a new model option, even the youth models will require a slight break in.