The specific cause of astigmatism is unknown. It can be hereditary and is usually present from birth. It can decrease or increase over time. - American Optometric Association
You might've had it since birth but without noticeable defect and has progressed rapidly enough to produce a defect in your vision during your early 20's.
Other factors that would ...
A toric lens is the type that is used to treat astigmatism, not an aspheric lens. An aspheric lens is primarily designed to correct for the spherical aberration of the contact lens itself, the spherical aberration of the combination of the cornea and lens of the eye, or both.
A toric lens is shaped like a slice of the side of a torus. It has a different ...
I finally found this:
Plano - PL - This indicates there is no spherical correction in this
eye. A plano lens would have no focusing power or correction to it.
So it's 0.
Source: How to Read and Enter Your Eyeglass Prescription - aclens.com.