In this day and age, depression ran rampant, but you'd never know it from looking at most.

There are two errors in your opening line.

(1) "depression ran rampant".

That's past tense, but you say "in this day and age", which is in present tense. So either say

In this day and age, depression runs rampant....

or remove "in this day and age" or use another phrase that is in the past tense.

(2) but you'd never know it from looking at most.

at most. At most what? looking at most things? Most people? This is an incomplete sentence. Either say "you'd never know if from looking" or complete the phrase.

You can't use just "looking at most" in English. "Most" is an adjective. It needs a noun to modify, like "people" or "places" or something.