@CookieMonster It is normal. Not a Japanese but can understand, i guess that is the norm for most Asian country,
At these time you rarely have time to hang out with friend anymore. School age is the time best for these active, So yes, it is very common to see grow up people say cherish about high school memory. Why ? this is the time to spare and have no worry about the life expend yourself. You can just be a kid, all carefree without a care in the world.
Once you go to collect or work, thing different now. Now each of you have go you own way. You also have no mood for these thing tbh, now need to life far from home which mean rent a room with monthly fee and no salary yet. And collect school is different, if you find friends the new school then it is good. But honestly it still never really the same.