"in the prime of one's age"是一个描述年龄与状态匹配的短语，核心含义是：
强调人在身体状态、精力、能力都处于巅峰的年龄阶段（通常指青中年，如25-45岁左右，具体因语境而异）。
prime：此处为名词，意为“鼎盛期、最佳状态”（the best or most active period of sb's life）；
one's age：限定“某人的年龄阶段”，突出“年龄上的黄金期”（区别于抽象的“人生鼎盛期”，如`in the prime of life`更侧重“人生状态”，而`in the prime of one's age`更强调“年龄层面的最佳阶段”）。
该短语通常作表语或状语，修饰主语的“年龄状态”，常见结构：
主语 + be动词 + in the prime of one's age
主语 + 谓语 + （时间状语）+ in the prime of one's age
① He started his company in the prime of his age (28 years old) and quickly made it successful.
（他在28岁的黄金年龄创办公司，很快就取得了成功。）
② She is still in the prime of her age—her energy and creativity are unmatched.
（她仍处于黄金年龄——精力和创造力都无人能及。）
③ The athlete retired unexpectedly when he was in the prime of his age, shocking his fans.
（那位运动员在年富力强时突然退役，令粉丝震惊。）
④ Don't waste your time—you're in the prime of your age and should pursue your dreams.
（别浪费时间——你正处于黄金年龄，应该追逐梦想。）
in the prime of life：更常用，侧重“人生的最佳状态”（不一定严格对应年龄，可指事业、健康等巅峰）；
at one's peak：更简洁，强调“能力/状态的巅峰”（可指年龄、事业、运动生涯等）。
"in the prime of one's age"是一个聚焦“年龄与状态匹配”的表达，适合描述人在生理、精力、能力都处于最佳阶段的青中年时期，用在强调“年龄优势”的语境中非常贴切。