Indirect fire was well known before artillery. Archers and siege engineers used it back as far as we have records. So I'm sure early artillerymen were able to do it.
As far as indirect fire becoming "standard," that's late. Like WWI late, where most artillery is located well behind the lines and fires at a co-ordinate rather than by the crew aiming at a point target. Through the 19th century most battlefield guns, or field artillery were fired directly at enemy formations, although siege mortars existed very very early on.
The big limiter on effective indirect fire is not the gun, it's communication between the artillery crew and the artillery spotter.