What are statistical odds for cancer returning in a 63 yr old woman 20 yrs after treatment for stage 1 breast cancer (lumpectomy, chemo, & radiation)?

Low, but not zero. First of all, congratulations on being a 20-yr survivor! it is impossible to give you a number or even a range without knowing more specifics about your cancer, however, the fact that it hasn't returned in 20 years certainly puts you in favorable statistical category. I suggest that you meet with your medical oncologist to discuss this, as well as any measures you can take to prevent a recurrence.
Very low, but. Sounds that you have been truly blessed with your life, and the chance is very low for the cancer to return but not impossible. Sometimes a different breast cancer could develop, even the kind could change it's characteristics; like hormone status.Typically, that would have happened sooner.The incidence of breast cancer in a woman goes up as she ages.You need to keep your ck ups, exams. Good luck.