velcome.

Possible air guns (assuming we are talking Spring power).

Webley break barrels (some come with open sights - NO scope required)

Hw99s With open sights.

If you are looking at buying a scope as well as the rifle then -

HW95 - Webley Break barrels as above - BSA lightening.

NEXT PRICE RANGE UP -
Air Arms Tx200 or TX200HC
Hw77k open sights
HW97k
These are all bigger and heavier rifles so you will have to think about any physical limitations of your son??

Regards

Michael