From what I was told by my parish priest when I asked him this question, is that there is no difference between a dioceasan and a religious priest on this subject. Priests cannot appeal for a dispensation until they turn 45 years old. The Pope is not the sole person to dispense a priest, the magesterium does this. A priest however at any time can resign and be laicized. But I am getting mixed messages from this thread, maybe I’m wrong, does anyone else know more about the process of a priest recieving a dispensation?
As for the subject of ex-priests celebrating mass and weddings, once the priest has been laicized, he is forbidden to present himself as a cleric and to celebrate the sacraments with only one exception (a laicized priest can administer extreme unction under the condition of if there was somebody about to die, such as a car accident on the highway, and there wasn’t a priest available.) Although a priest has been laicized, he still bears the mark of the priesthood on his palms, any sacrament celebrated by a laicized priest is valid, but illicit, due to disobedience to their bishop. The only exception is what I already mentioned.