Depends upon the person and the air rifle.
I recently wondered, after seeing another Long Range Shooters of Utah YouTube video in which a guy even used a “pistol” to hit a milk jug at 1000 yards, what would be an equivalent range and size target for air rifle users. I don’t entirely approve of spotting for the shooter, or indeed helping a shooter in any way, such as LRSU do.
For approx 900fps rifle users, and given the skills and variables effecting such pellet drops, I think that 150 yards for a golf ball would be an equivalent test. However, in general, I think that beyond 100 yards has to be considered long range. Ted's videos of one hole groups at 100 yards may make some people think that such is easy, happens every day, that all you need to do is buy a Bobcat & other equip and that they will automatically become such a shooter and produce such groups everyday.....but the reality is usually different.