Working with my practice file, I've discovered that even with all needs met, the right emotion, requirements satisfied, and picking the right option on a chance card, it takes about 2 workdays to get a promotion. With an age span of 42 days, that would suggest that even a good player is not going to be able to max more than 4 careers for two sims.
On the long age setting, there are 80 or 81 days from young adult to adult. I think there would be more variation in scores if you went to a long age setting ending at Adult, but it may be too late to make this change in the rules.