I have a hankerin' for a CZ 457 Varmint to do some cheap plinking and get my 8 & 9 year olds involved.  I started shooting when I was 6 but didn't shoot a rifle until I was 18 , so I don't really have a frame of reference to determine how big of an issue LOP would be for a kid.

Why not buy the gun and find out?

Get the Scout version (12-1/2"), or they have a new chassis that will take an adjustible AR-15 buttstock.

Whats age got to do with it?

If it bothers you that bad. Measure their LOP's. Generally, any rifle you buy will have a standard LOP of 13.5 inches because it's the most common LOP.

All depends on what kind of rifle, how big the kid is, and what you expect them to do with it.

I started shooting an M1A around 14, before that it was always a 10/22.  I've gone with youth stocks for my kids until around 12-16 years of age, depending on the kid.

Measure from the crook of the elbow to the last joint of the pointer finger, and set LOP to the shorter of the two boys.  It's way easier to shoot too short of a rifle than too long of one.

A lot of current rifles also have adjustable LOP, so they grow with the kids -  definitely a good plan.

"Youth" LOP is typically anything under about 12", normal is 12-14, and over 14 is long.

According to that method I would need a 15" LOP?  Seems strange because I'm known for having really short arms

It's best to do it on a gun, but you want the pad of your finger to rest on the trigger face without any stretching or contorting - then lop is actually from the face of the trigger to the rear of the stock.

Measuring your arm just gives you a ballpark of whether you should be looking at a youth stock or not.

But always come back to too short is better than 1/2" too long, and if you're going to shoot in heavy clothing that throws everything off.  I have a target rifle with a 14" LOP and a hunting rifle with a 12.5" - but I can still shoot the hunting rifle off the bench, I couldn't take the target rifle hunting.

I learned how to shoot with a Red Ryder.  Carried one everywhere when young, got so good with it I could have joined Buffalo Bill's show.  I still prefer a short length of pull.  I think it's all good as long as it's not too long.

Depends on the Child's Age, Gender (Boys & Girls grow at different rates & to different final size), and Genetics.  Look at yourself & your "Baby Momma", (along with your parents & her parents and that may give you some idea about estimated final sizes.

I put my son on a Youth Stock Set for his 870 until he was 14 (he grew fast).  I moved that same youth set to my daughters 870 & she is 26.

Shit I'm a fully-grown man and I think the LOP on my 870P is too long.

Hogue tactical entry short LOP 12" stock or Magpul stock in short configuration ftw.

Get them an AR15 in one of the myriad of available calibers, especially .22LR. It'll be good from 5-ish to whenever.

Already have 3, looking for something different.

It's really height, not age.  A 5.0 ft tall person is probably always want to stick with a youth model.

Note - not all youth models are created equal.  Cricket, Chipmunk,  and Savage Rascal all have a length of pull of 11.5, and that's find for a 5 year old to about 7 or 8.  Really more height/arm length dependant, but just realize it's not a 'normal' youth gun.

CZ-scout is slightly longer at 12.0, so maybe it will work up to about age 11.

Ruger American CoMPACT, Savage BF 22 COMPACT, and Savage Mk 2 GY have a 12.5 to 12.75 length of pull.  This is short enough that a kid age 9-10 will be fine using it, and will work great for kids up until their late teens.  In fact, if someone never grows much beyond about 5'4" or so, this is probably a size that will fit them for life.

Adult length of pull is 13.5 to 14 depending on manufacturer.  So you probably want to stay away from this until the person is hitting 5'6" or so.  Again, it's really arm lenght.  A kid that comes from a family that grows tall, they'll likely have longer arms at 5'6" on their way to 6'6" than a kid who'se likely to not ever get much taller than 5'6"

A lot of 'lady' models have 12.5, 12.75, and occasionally 13.0 LOP, again because it's not age based but height or really arm length.

Ever try and shoot a Cricket as an adult?

Yea, I'd rather shoot a stock that's a half-inch too short than a half-inch too long....but there absolutely is such a thing as too short.