Will the person who repented from abandoning prayer at an early age and became committed to his prayers and reading the Qur'an be punished in the grave or in the Fire?

If repentance fulfills its conditions, namely remorse for the sin, desisting from it, and resolving not to return to it, then it is accepted and erases the effect of the transgression, as if it had never occurred. Its doer will be saved from the torment of the Fire and the grave.