PSU had upper classmen on their defense this past year. From their offense, they only lose one starting offensive lineman, plus Gesicki, Barkley, and Hamilton. Not big in numbers, but those are big shoes to fill. The guy that will be the hardest to replace will probably be Gesicki, based on who's behind those guys. Barkley's the obvious huge talent, but Sanders will do OK next year, Slade will play as a true freshman, and they are loaded with skill guys at WR.
Different story on defense. They lose both starting safeties, both corners, the MLB, and two defensive tackles. The guys who will fill those positions are all 4 and 5 star guys, but that will be a young secondary and linebacker core. Their best corner missed all of last season with an ACL, so that will help.
Nowadays, all good teams are young, since players leave early regularly. Which is why recruiting better than 3-star guys is so important, because the 3-star guys aren't ready to play early.