The age of the engine has nothing to do with why camshafts are ground on an advance. The reason is very simple People always tend to overcam an engine. So, to compensate for that, grinders through the years have learned to grind 4* advanced in the hopes of picking up some of that bottom end torque lost to an otherwise poor camshaft choice.
100 % agreed.... don't let poor customer choices ruin your cams' reputations! It's the only reason that makes sense to me why this is done so commonly nowadays, but was not done 'back in the day'.