I just googled it and Pit is 44% male and 56% female. (33% more)
Purdue is almost the opposite and 42% female and 58% male. (38% more)
The effective opposite sex dating pool is even more skewed when couples pair up the remaining pool becomes even more out of balance. For example if 10% of both men and women are in an opposite relationship then for Purdue the remaining available students who are not in a relationship would be 32% female and 48% male, so there would be 50% more available men than women.
I would not suggest that the gender ratio should be a high criteria in selecting a college but it would be good for him to not underestimate it especially if he is not very socially outgoing like CS students of both genders are stereotyped to be.
It was decades ago but I got a BS in CS at a state STEM campus where the ratio was even worse where there were something like 8 guys for every girl. You can get some odd social dynamics when the balance is that lopsided but even lower imbalances could impact the kids social development and there is more than grain of truth in the computer geek stereotype.
I had gone to the state flagship university which had a bit of a reputation as being a party school for the first two years before I changed majors and transferred to the STEM campus. By then I had a chance to develop more social skills than I had in high school and if I had gone straight to the STEM campus developing those social skills might have been a lot different.
There is a line from an old movie about a gender imbalance that the women would sometimes mention which alludes to this, "The odds are good, but the goods are odd."