The phrase "after one is" is correct and usable in written English.
It can be used in contexts where you are discussing a condition or situation that occurs following a specific state of being or action.
Example: "After one is fully prepared, they can confidently present their ideas to the group."
Alternatives: "once one is" or "after a person is".
For this is the lesson passed on to future generations, long after one is gone.
After one is injured, his son arrives to take his place.
Of course, a situation where extra parents suddenly turn up after one is fully grown lends itself to strangeness, almost to kitsch.
"Tanna," filmed mostly in Mr. Dain's tribal village and the surrounding jungle, chronicles the fate of two star-crossed lovers who rebel after one is steered into an arranged marriage.
Follow up procedures such as continued rehabilitation to reduce possible gait deviations and maximize functional potential, may reduce mortality given death often occurs approximately 1 month after a hip fracture, which is after one is discharged from the hospital (Shumway-Cook et al. 2005; Studenski 2013).
Even competitive news organizations, at times, have acted collectively after one is sidelined over claims of unfair coverage.
In 1944, the Secret Service caught wind of the purloined coins after one was successfully sold to Egypt's King Farouk.
Two Israeli Arabs traveling with her in the car were arrested after one was shot and wounded.
Keeper Jimmy Nielsen needed stitches after one was thrown at his face –police charging a fan with "felony aggravated battery".
The two men fled after one was wrestled to the ground by the store's owner, the police said.
But that's very strained, especially after one's read the surrounding context of this passage and has also discovered what's usually meant by such phrases.
