In 2017 when you first asked for advice, he was (at least) in ninth grade. That means he is (at least) a rising senior.
This was the advice given by a senior poster back in 4/17:
"First things first.
He hasn't played in a long time.
Get him signed up for whatever school, travel, or rec team he can get on.
See how he stacks up and whether he still likes the game."
By your last post, he hasn't done anything baseball-wise in the over two years since your last topic.
Now, onto your questions.
During pre-HS years, one of the family pursuits was MILB; S and I (dragging M and D along) would arrive in time to stand outside the stadium and snag BP HRs. Over the years and hundreds of games, we collected hundreds and hundreds of balls. By the time he hit HS, the earliest balls were well over five years old. Never had an issue with old balls; so, no, the age of one's balls is irrelevant (now, if the balls got wet/waterlogged that is different).
You specifically said "he want[s] the truth."
Here's the truth: THERE IS NO WAY HE CAN USE BASEBALL "TO GET TO COLLEGE." PERIOD. FULL. STOP.
First, he clearly has no love or desire to play baseball (even at the HS level). Second, he has no baseball skill set to offer. Third, he has no measurables. Fourth, HE DOESN'T PLAY BASEBALL AND HASNT SINCE LITTLE LEAGUE. Fifth, he has taken no lessons to develop his skills. Sixth, you don't seem to want to understand that of 430,000 HS players, 38,000 go on to play college NCAA baseball - and your grandson isn't even one of those 430,000. These aren't odds stacked against him; a power ball lottery ticket has a better chance.
Look, this may come off as harsh, but it's an absolute insult to not do anything in baseball - not play, not take lessons, not ANYTHING - and think he can somehow, someway use baseball to leverage his way into college. (Also, there is no demonstrated understanding of how hard HS players must work just to have a whack at college ball; much less what it takes to play CB.)
He wants the truth? Become a fan, support the HS team, get good grades in college, play catch with his son or daughter when the time comes.