20/20 vision all my life, suddenly doc says20/50 & astimatism n both eyes. really? is this possible? if so, y?

Yes: You have probably had the astigmatism and now as you age your muscles in the eye are unable to accommodate for it. Now it is manifesting. Checking for it in the past though dilating you eyes and checking a refraction would probably have revealed this. It would not have been treated until it caused a problem (headaches or blurred vision). Rarely astigmatism develops over time.

Lens Changes: It is not uncommon that individuals with excellent vision hitting their late forties-early fifties suddenly develop blurred vision. It is often related to lens changes that are progressing to early cataracts. The prescription changes can take the form of nearsightedness, farsightedness, and/or astigmatism.