How many glasses of water is good for a 19-year-old boy to drink day and night? and what kind of disease can be caused by drinking more or less water than necessary?

About 6 eight ounce glasses a day is reasonable. Too little water intake leads to deydration & kidney failure, too much leads to too much urine volume loss causing electrolyte imbalance, bets are off if diseases like diabetes mellitus or diabetes insipidous are causing excessive thirst or excessive intake of fluids, symptoms which warrant a evaluation by a physician or endocrinologist

You need to consume enough fluid to pee every 6 hours. Many foods have fluid value, which adds to the daily water load. Counting glasses/ounces is a rather pointless exercise. If you don't pee in 8=10 hours you are dehydrated, drink too much water and you spend excess time in the bathroom.