No discrimination Frank, just the rules. And understandably so too.
From the Civil Aviation Safety Regulations 1998:
Part 67.205
(3) Subject to subregulation (6) and regulations 67.215 and 67.220, a
medical certificate issued by CASA to a person who has undergone
any relevant examinations required for the purpose of the issue of the
certificate remains in force for the period set out in the certificate,
being a period of not more than:
(a) in the case of a class 1 medical certificate — 1 year after the day
when the certificate comes into force; and
(b) in the case of a class 2 medical certificate:
(i) if the person is less than 40 years old when the certificate
is issued to him or her — 4 years after the day when the
certificate comes into force; or
(ii) if the person is 40 years old or older when the certificate is
issued to him or her — 2 years after the day when the
certificate comes into force; and
(c) in the case of a class 3 medical certificate — 2 years after the day
when the certificate comes into force.