Augustine of Hippo

It is usual for the prophets thus to mingle metaphorical and literal expressions. Yet, anyone with serious purpose and a little useful and salutary effort can discern the prophet's spiritual sense; it is only a lazy and worldly person or one who is ignorant or uneducated who will rest content with the literal and superficial sense and refuse to penetrate the deeper meaning.

City of God 20.21 ↗

Jerome

And there shall no longer be heard in her (in him) the voice of weeping, and the voice of crying. There shall no longer be an infant of days, nor an old man who has not filled his days. For the child shall die at a hundred years old, and the sinner at a hundred years old shall be accursed. LXX: And there shall no longer be heard in her the voice of weeping, and the voice of crying. Neither shall there be any more premature and old person who does not fulfill their time. …

Commentary on Isaiah ↗

Thomas Aquinas

Second, as to length of life: there shall no more be an infant of days there, nor an old man that shall not fill up his days, dying before his time, but the child shall die a hundred years old, that is, when he will have reached such an age; and, if he be a sinner, although he will have lived to such an age, he shall be subject to a curse: Abraham died in a good old age (Gen 25:8). …

Commentary on Isaiah ↗