The 54's are nice, they are a very big and heavy rifle. Depending on how old your boy is it may be a lot to handle. Had I seen this thread earlier I would have suggested a Beeman R-9. The R-9 is a much more compact and lightweight package. Still shoots 675fps w/ 14.3gr pellets and thumps rock chucks by the truckload.
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A true sportsman counts his achievements in proportion to the effort involved and fairness of the sport. - S. Pope