With ordinal number, usually following a possessive adjective: a specific twelve-month period in the lifetime of a person or animal, as reckoned…

with ellipsis of years (referring to age). Now rare except in threescore, adj. and fourscore, adj.

Seventeen years of age.

absol. with ellipsis of years, in reference to age; hence as n. the age of sixty years, or transferred a person of this age. So threescore (years) an…

A fiftieth year. Obsolete. rare.

the age at which a person becomes eligible for military service; the age range within which a person is eligible for military service.

(a) the age at which a person's participation in a particular activity or appointment to a specific role is legally valid or permissible (cf. age, n.…

†(a) the age of a father at his eldest child's birth; (b) child-bearing, pregnancy.

Sixty years of age. Also sixty-one, sixty-two, etc.

The age of 40 years.

The age of fifty years.

(a) adj. that is seven years of age; (b) n. a child, animal, or thing that is seven years of age.

In expressing the age of a person (rarely also of a thing): any of the years whose numbers end in -teen… In singular. Obsolete.

the state of being a septuagenarian.

the state of being a sexagenarian; character or behaviour suggestive of a sexagenarian.

(a) adj. (attributive) designating a person, animal, or thing that is one day old (cf. old, adj. 4b(a)); (b) n. a bird, animal, etc., which is one…

(a) adj. that is seventeen years of age; (b) n. a person, animal, or thing that is seventeen years of age.

the state or fact of being a centenarian.

figurative. The fifth decade of life, esp. regarded as a period of vigour and activity.

plural. The numbers from 20 to 29; the years in a century or of one's life, or the degrees of any scale (e.g. of a thermometer) so numbered.

the age at which a pupil is legally entitled to leave school for good.

= leaving age n. at leaving, n. compounds 3.

The state or fact of being an octogenarian.

reading ability expressed by the developmental age (in terms of the national average) at which comparable ability is achieved.

Absolutely or with ellipsis of the noun (most often persons; otherwise to be supplied from context).

The period of a person's life between the ages of thirteen and nineteen inclusive, the teens; an age falling between these limits.

the age (between 11 and 12) at which pupils leave primary schools; also, an examination taken at the same stage before entering one of the various…