Could've gone another way:

He studied medicine at the University of Colorado at Boulder but was keener on the stage than becoming a doctor. O'Brien switched to civil engineering under his family's guidance, but his heart was still set on becoming an actor.

You can hear the poor parents' lament: at least finish school so you'll have something to fall back on! Lucky for him, the acting biz worked out, and he had a good run in the late teens and 20s. Reviewing The Only Woman, the NYT critic really poured it on:

Although the actual plot of Norma Talmadge's latest film vehicle. The Only Woman, is not unfamiliar, the story contains several interesting situations which are effectively pictured.

That's my new term for a good movie: "Effectively pictured."

Anyway, O'Brien bowed out of the business after sound, and never made another movie.