How does one repent from conversing with a young man while knowing its impermissibility and delaying repentance for it, and will this repentance be accepted and will Allah forgive the sin after it is too late?

Repentance is accepted from whoever performs it fulfilling its conditions: namely, abstaining from the sin, resolving never to return to it, and regretting having committed it. So, whenever these conditions are met, repentance is valid and accepted, and the one who repents is like one who has no sin. The time for repentance does not expire as long as a person is alive and the soul has not reached the throat.