A retired priest and a laicized priest are not the same thing. A retired priest is a priest who has, well, retired. Usually due to age or poor health. Just as anyone might retire. They are still priests, and usually contine to help out in parishes and other apostolates as their time, health, and inclination allow. They may be given light duty or no duty by the bishop, according to circumstances and need. Their vows of celibacy and obedience still apply.
A laicized priest is a priest who has been removed from the clerical state. That is to say, he is still a priest, but from the point of view of church law and discipline, he is treated as a lay person. Thus, while he still has the powers of a priest, because he is still truly a priest, he is no longer permitted to exercise them except in the most extreme circumstances. When a priest is laicized, it can be because he has asked to be, or it can be a punishment for a grave offense, such as sexual child abuse. In either case, the laicized priest is usually, but not always, released from his vows of celibacy and obedience to his bishop.
If a retired priest says Mass, it is both valid and licit. If a laicized priest says Mass, it is valid, but illicit. It is valid because the bread and wine will be transformed into the Body, Blood, Soul, and Divinity of Jesus Christ. But it is illicit because he is no longer permitted to say Mass. It would be a grave offense.
Still, in truly extreme circumstances, a laicized priest may licitly administer the sacrament of reconciliation. Such would be the case if he found himself on a doomed airplane. He could (and should) give general absolution to those who wish to receive it. Or if he comes upon a car crash, he could (and should) hear the confession of a dying victim.
This is because once a man is ordained a priest, he is a priest forever, into eternity. Ordination as a priest imposes an indelible mark on his soul, which no power in heaven or on Earth can undo. God Himself has made him "a priest forever, in the line of Melchizedech."