of age—
1. having reached a certain age:
- All children must receive full-time education until they are at least fifteen years of age.
2. legally an adult:
- The legacy left him by his father is in the hands of trustees, as he is not yet of age.
Note: The expression is not equivalent in meaning to the phrase of one’s age—used of a deceased person’s age on memorials, obituary notices, etc.:
- He came to this county in the year 1836, and was, at the time of his death, in the 69th year of his age.
of an age—
1. having reached an age when one is old enough to do smth.:
- The eldest boy Charles was of an age to be flying off and building a nest of his own.
2. of the same age:
- I got more mental stimulus from some of my school-fellows who were of an age with me.
Note: The expression does not correlate in meaning with the phrase of a certain age—(euph., of a woman) no longer young; middle-aged:
- One sometimes sees women of a certain age who are still very beautiful.