Can someone give me a timeline concerning freshmen being unable to play college football?

You are correct, there was a time Freshman were not allowed to play, and guys had only 3 years of eligibility. That changed about 1973. So legends like Roger Staubach and Jim Brown didn't get a whole 4 years to play. That's why most career-type records and all Freshman records are owned by guys who've played in the past 30 years.

(Somebody have me a thumbs down for this?? Now that's class.)

freshmen play college football it's just that most of the time the team already has an older more experienced player in that position so they red-shirt the freshman, however some do get to play. look at colt mccoy he was the starting QB for texas this year as a freshman.

I don't think there is any rule regarding freshmen being able to play. It's just that they are only allowed to play for 4 years total, and since they normally graduate in 5 years, it's better for them to red-shirt the first year so that they can mature and play the remaining four years.

I've never heard of that rule. Are you talking NCAA division 1?

Some schools feel that athletes coming straight out of high school are not developed enough to play their first year and will therefore redshirt them to give them more experience and time to adjust to college life.