What factors are considered by courts to determine whether a person over 45 has a valid claim for employment?

In terms of the age factor, in McKinney v. University of Guelph, 1990 CanLII 60 (SCC), [1990] 3 S.C.R. 229 at para. 92, La Forest J. observed: that Barring specific skills, it is generally known that persons over 45 have more difficulty in finding work than others. They do not have the flexibility of the young, a disadvantage often accentuated by the fact that the latter are frequently more recently trained in the more modern skills. Their difficulty is also influenced by the fact that many in that age range are paid more and will generally serve a shorter period of employment than the young, a factor that is affected not only by the desire of many older people to retire but by recruitment policies both in the public and private sectors.