在二十多岁时英语

at one's twenties

in his twenties是固定句型,更多含有“二十几岁”的意思,换而言之从额21 到29都可以包含,所以是用众数twenties,如果指明是二十岁的话,用twenty years old会适合点,即when he was twenty years old 或when he was twenty

一般来说是 20s，但也有说美英 20's，英英用20sIn British usage, we do not use an apostrophe in pluralizing dates: This research was carried out in the 1970s. American usage, however, does put an apostrophe here: This research was carried out in the 1970's.其他来源的解释：The Chicago Manual of Style recommends no apostrophe is something like 1960s.Ages are the same kind of thing. Consequently, the better form is:This is her brother WILLIAM (30s), fat, poorly dressed.所以最好不加撇号（apostrophe ），用20s

in one's twenties

inone'stwenties