The legislation states:
(2) A person is qualified to act as an accompanying driver if he or she,
(a) is a fully licensed driver in a Class G motor vehicle;
(b) has been licensed in Ontario or another jurisdiction for at least four years; and
(c) meets the applicable requirements of the Act and the regulations, including any requirement to wear corrective lenses but not including any requirement for any special or modified controls applicable to the accompanying drivers licence. O. Reg. 340/94, s. 5 (2); O. Reg. 83/05, s. 4; O. Reg. 205/10, s. 2 (2).
http://www.e-laws.gov.on.ca/html/regs/e ... _e.htm#BK0
I would keep a copy of that in your car, but how are you going to prove that your father has been licensed for 4 years?