Today, one in every ten is 60 years and older. By 2050, one out of every five will be an older person, and by 2150, one third of the people in the world are
expected to be 60 years of age or older.
In our fast ageing world, older people will increasingly play a critical role - through volunteer work, transmitting experience and knowledge, helping their families with
caring responsibilities and increasing their participation in the paid labour force. Older persons make major contributions to society. (...)

The article:
http://www.hrea.org/index.php?doc_id=869

More about:
http://www.un.org/en/events/olderpersonsday/
http://www.who.int/ageing/events/idop_rationale/en/index.html
http://www.who.int/ageing/en/

An interview:

http://www.un-ngls.org/spip.php?article3591