Other than having a natural interest, which would already be manifest, there are only 3 motivations for an 18 year old to spend time to learn something.

Since programming is unlikely to save his life, or get him laid, you're left with the profit motive. Few 18year olds have sufficient cash to fund their ambitions. If you are in a position to allow him to earn some cash by programming, it might result in a residual interest.

Whatever you do, don't try pushing the OSS altruism ideal. The logic (or not) of that is very much a personal decision/choice, a bit like religion 'cept maybe more so.