When should someone start learning sidespin (AKA english)?

I don’t think a person should spend much time with sidespin until his or her fundamentals and stroke are solid. Also, CB control with stun, follow, and draw should be mastered first.

When deciding to use sidespin seriously, a person should also start learning about all of the effects (squirt, swerve, and throw) that need to be taken into consideration. Otherwise, they will miss many shots when using sidespin which can make them lose confidence, and their learning process (through trial and error) will be much slower. For more info, see aim compensation for squirt, swerve, and throw.

Concerning when sidespin should and should not be used, see the Sidespin Tutorial and the Sidespin Examples resource pages. See also:

from Bob_Jewett:

As far as the basic knowledge part, I think it is important to discuss that before the beginner starts using side spin. I point out how the side spin can be useful but at the same time I show five major problems with using it: squirt, swerve, throw, miscues and cling/skid/kick/bad contacts, and some of the details of those problems. Most beginners do not fully understand those problems when first introduced to them, but I want them to be aware that problems exist.