The bantam has a 12 inch LOP for a youth, but does adjust as the youth grows to a 13 inch LOP.
The gold Standard is taking the measurement from elbow to trigger finger to find your LOP. But I find this misleading simply because it doesn't take thick winter clothing into the equation.
Chances are you will not find a perfect fit since there is standard youth LOP stocks and same for adults.
With the adult you can always have or cut it down your self to fit so I would look for an adult sized shot gun if your a adult that has stopped growing.
Also don't be letting people talk you into buying a 12ga if your an adult, a 20ga is a fine shot gun for any age old enough to use a shot gun. With todays screw in chokes and different shot shells they will do about any thing you want.
Also keep in mind Multa barrel shot guns are usually a barrel for shooting shot and a second barrel for shooting slugs. If all you want to do is shoot shot then a barrel with screw in chokes is desirable to have. A selection of chokes from a full for duck and goose hunting longer pheasant shots, down to a open choke like skeet or imp cylinder for closer game like rabbits and grouse.
My self I would spend a bit more at a gun shop that will try to fit the shot gun to your stature. I also feel money spent on a Remington 870 well spent. You will get that extra spent back when and if you sell it.
I would chose the 26 inch rifled barrel model unless your going to deer hunt in a blind or thick woods.
https://www.remington.com/shotguns/p...-express-combo

Al