unless it's a surprise gift, take him to the store and have him shoulder it, look for signs of any struggling or discomfort with the rifle. kid's come in different shapes and sizes too, perhaps a youth rifle that is designed to fit the masses may bee too small or too big for any 1 kid.
google fu the Length of pull of what fits. if there's a type of rifle mentioned in this thread that is not on the shelf, at least you'll have a good idea if one is going to be too big or too small.
if you want to keep the rifle "as is" and not cut anything - and if it fits - i really like the ruger american compact's size, ability to lengthen the pull in about 2 minutes. the finish of the metal, quality of the sights, bolt angle, etc. is really nice for the price. lots of features to it either open sights or scoped, adjustable trigger, etc. - i'm really impressed with mine, and it's pretty accurate on top of it (really like eley target yellow box), and handle bulk ammo well too. you can get a single shot adapted magazine if you want to go that route, or keep as a repeater.
the CZ scout is a whole lotta rifle for the price too, that is if it's going to fit. can just buy a magazine to have it be a repeater. either the CZ or RAR would make a fine rifle for a Youth rifle that would probably remain in the safe for years. i think the CZ scout receiver could be bolted to a standard sized one later, but not 100% sure.
the rascal has a surprising amount of features to it too, but once he grows a bit, it's on to another rifle as the receiver is shorter than the standard MKII and can't be bolted up to a standard stock.
marlin / rem 915 doesn't have the front mounting screw, much like the old model 25, but is single shot. you may not be able to bolt that up to a standard stock later, though a XT22Y compact in synthetic has it and you can change it up later with a replacement stock and is a repeater.
cricketts are nifty, but again, once outgrown, it may be time for another rifle. they do offer replacement stocks, but i don't know if they are full sized. single shot and manual cocking with the knob on the back.
i think the most versatile out of the bunch is the RAR and CZ scout with "big gun" look, feel, and designed to grow with a shooter.