Wiktionary
n. (context idiomatic English) The period of one's mature life when one is at a peak of health and performance
WordNet
n. the time of maturity when power and vigor are greatest [syn: prime]
Usage examples of "prime of life".
I was at that time about four- or five-and-thirty, in the prime of life, in fact.
Righelini, who died in the prime of life, and whom I still regret.
The rectangular room was spacious but furnished only with a large, plain wooden table, two stuffed armchairs not in the prime of life, and two straight-back chairs.
Even more mysterious is that it was primarily devastating to people in the prime of life.
She was past the prime of life, with gray showing in her elaborate coiffure and two coarse black hairs growing out of her chin, but the precious rings on her stubby fingers and the gleam of gold weighing heavily at her neck indicated her rank.
Although if they die old and decrepit they often return looking as they were when in the prime of life.
If that should prove the case, then at least it would be a noble close, for it was a fine great generous wine in the prime of life, one that could stand being tossed about at sea: they drank it slowly, not saying much but sitting there in a companionable silence in the candle-light while the ship moved steadily inshore.