I see where your friend is coming from and I see his comments as anti-ageism rather than anything else but if he's said the same thing about women (taking time off because of sick kids etc) then it would be seen differently. We have to be careful how we generalise in a work environment. I find Eastern Europeans have a better work ethic and are more skilled than their Irish counterparts but that does not mean I wouldn't take everyone on a case by case basis. I presume your friend operates with the same attitude when it comes to age.You are getting ahead of yourself here. He doesn't discriminate against young people. He has about 6 teens and 20+ employees on his books.
He would prefer to have more mature staff. He considers them to be more reliable, better productivity, less supervision. That is his opinion.
He finds it hard to find these worker's. Probably due to the wages (more or less minimum wage) he offers. Perhaps he can't afford to offer higher wages, perhaps he is tight with his money. Either way it's his business and he gets what he pays for.
There is no discrimination case here. There would be if he refused to employ someone on the basis of what age they were.