pcp for 8 yr. old boy?

Only suggestion I have is look into a sidelever rather then a bolt action, reason I say this is because I tried twice to set up Marauder pistols as rifles for my daughter and the bolt action was to much, ....Sidelever actions are wayyyyy smother and easier to operate.

LOP wise, a wood stock would be easy to cut down for a kid or a rifle with a collapsible stock like the Kral NP3 that also has a sidelever and power adjuster so can apt for a lot of shots if want.
 
Maybe check out pcp pistols . Crossman makes a few and a butt stock for them . not much money and light weight , good for starters an 8 year old does not like to carry a 8 pound gun . Crossman also makes a pump pistol 1377 0r 1322 3 pumps not hard and good for 10 yards paper 8 pumps and good for 20 yards or more. i think $ 69 plus butt stock $20 ?

lGoogle "my 1377 custom i built " plenty of show off's and information .
 
Hello Had a Prod for a while and a very nice little gun to start off with. Light, good trigger, easy to pump w/hand pump or 34 fills from a standard 3000 psi scuba tank (with a 2800 to 1800 psi fill) many stock options for length of pull(ar stocks w/ adapter, TKO22, or just an old Crosman one cut down), and 32 good shots per fill. With a red dot or a bug buster scope good out to 30 yds or so. Well best of luck on what you decide, any question just ask Eric
 
I bought a talon p frame and a 20 cal barrel for my daughter who was 8 at the time. It worked perfectly. Not only can you adjust length of pull but you can change the top hat and hammer spring to make it as weak or powerful as you want. I highly recommend it. Also a single shot is safer for kids IMO. I'm getting almost regulator consistent strings by putting an oring behind the top hat. 
 
Just measured my Fortitude And the length of pull is 14 1/4 inches.In comparison a daisy model 25 which is mostly for kids is 13 1/4. Which the Daisy fit me fine at age 6. The fortitude is very light also.The only thing you would have to be careful with is making sure he understands how to load the magazines and also fill the gun up with air.It’s not too bad cocking the bolt back but a side lever is much smoother.