The Right to non-discrimination on grounds of age is explained in these documents:

Legally Obligating Documents
African (Banjul) Charter on Human and People's Rights (3, 18(2))
Convention on the Rights of the Child (2(2))
International Covenant Economic, Social and Cultural Rights (2(2))
International Covenant on Civil and Political Rights (2(1))

Standard Setting Documents
Beijing +5: Further Actions and Initiatives to Implement the Beijing Platform for Action (32, 33)
Beijing Platform for Action (83(k, l), 106-08, 281)
Cairo Programme of Action (7.41, 7.45, 7.46)
UN Special Session on HIV/AIDS (UNGASS) Declaration of Commitment (63)
Universal Declaration of Human Rights (1, 2, 6)