age twenty; one's twenties
A somewhat literary or old-fashioned way to refer to the age of twenty or the decade of one's twenties. In modern Japanese, 二十歳 (はたち) is more common for the exact age, and 二十代 (にじゅうだい) for the decade.
She is still young, in her twenties.
When I had just turned twenty, everything felt fresh.
The standard modern word for one's twenties as a decade. 二十路 can also refer to the decade but is more poetic.
An old native counting expression: ふた “two” plus そじ, a form used in traditional words for multiples of ten. 路 is a conventional spelling of the latter element.