> Foreign languages are harder to pick up the older you get.
I don't buy that. I know plenty of people who've picked up languages all up and down the age range.
What I do think is true is that people are more likely to pick up their first additional language at a younger age. And I think that that's probably just an result of selection bias: If you actually need to for some reason (e.g., one language spoken at home and another in public), then those conditions will apply more-or-less from birth, so you'll learn it at a young age. And if you enjoy language learning, then you'll probably figure that out at a fairly young age, and so you'll have learned your second language at a fairly young age.
The people who're looking to learn their second language in their 30s or 40s, on the other hand, are likely to be less motivated in the first place, and therefore more likely to give up, or to be unwilling to put enough work into it to make consistent progress.
There's also a sort of. . . I don't know if it's immortal time bias, but it's similar: You don't see as many people who learn a language at an older age exhibiting near-native levels of proficiency simply because the timeline doesn't work out that way. You just aren't going to be speaking like someone who's been using the language 16 hours a day for 20 years if you've only been using it 1 hour a day for 5 years. Anyone who tries to tell you otherwise is probably selling something with a subscription pricing scheme.
I can also say, as a recreational language learner who is rapidly approaching middle age, that the real impediment to learning languages as you get older is not that you don't have a 6 year old's or teenager's brain anymore. It's that you have one or more 6 year olds or teenagers, and spending time with them is probably more fulfilling (or at least more important) than spending time with a pile of flashcards. Such is life.
As far as the value of requiring them in university. . . Offer, yes, require, no. Not because 18 is too late to start learning a language, but because nobody who's only taking classes in a 2nd language because a few credits in such a class is required for graduation is going to get any real value out of the experience.