Its gravity. The further the pellet travels the more it will drop. You will need to adjust your aim higher the further out you are shooting. This is why you have the extra hash marks on your scope so you can adjust your aim and have a reference for the future.
It wasn't removed just locked with moderator explanation as to why the post violated the rules https://www.airgunnation.com/topic/finnally-my-aea-35-cal-big-bore-is-quite/?referrer=1
GX compressor $369.99 https://www.amazon.com/dp/B07XYRS15R?psc=1&ref=ppx_yo2ov_dt_b_product_details Can do your filling at home or in the field with 12V Air Venturi Avenger $349.99 https://www.pyramydair.com/product/air-venturi-avenger-regulated-pcp-air-rifle?m=5136 If you don't already have...
I would just get a compressor. No need to worry about getting the tank filled you can fill the gun directly at home or some connect to 12V for filling from your car battery.
I am surprised at the amount of sellers requesting to use Friends and Family for payment in the classifieds. I understand there are fees involved but that should just be included in the price. Way to risky to send over $1000 to a seller with no protections...
If you want full auto and have $800 to spend you can get a refurb Hatsan Blitz from their site https://hatsanairgunsusa.com/product/refurbished-blitz/ I don't believe you can use a suppressor on them so that may be a deal killer for backyard.
I have this one coming tomorrow https://www.amazon.com/dp/B08PL22NNW?psc=1&ref=ppx_yo2_dt_b_product_details clams to be rated for rimfire the .25 cal has been brutal to the standard pellet targets.
Agree it may depend on the individual kid and the amount of time the parents have spent training them. Still think 9 would be too young due to the risk involved especially with a buddy.