Can too much caffeine kill someone?

Possible. If you have a medical issue like heart condition for example.
Very very rare. Mainly because very high doses of caffeine usually result in so much nausea that the person cannot take in more, or vomiting which reduces absorption. However, nicotine is a poison, and certainly can cause death in extremely high doses. There have been a handful of deaths reported(actually several handfuls) in people using high-caffeine energy drinks, especially younger people (your age ; younger).