Back in the Walsh era it likely would have required a few starts as a Freshman since many teams only played 11 games per year. Which is more rare since freshman often times did not play back then.
I also think that modern offenses are designed for QBs to play earlier. We see success from young QBs all the time now because modern offenses simplify the game for them with RPOs and half-field reads. But I can certainly see why Walsh would want a guy with as much experience as possible to run his offense.