Catechism of the Catholic Church §1528 — excerpt
The proper time for receiving this holy anointing has certainly arrived when the believer begins to be in danger of death because of illness or old age.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.