Good to hear that you have an interest in Bitcoin, 18 years old and already invested on it. Being a courageous to try new technologies, i mean new innovations, crypto investments, thats a good sign for potential high returns in a long term investment.
But take note about the security risks, you have to secure your bitcoin to prevent losses and to be safe from hackers.
This is the right age to step into crypto world, he will earn handsome amount in near future if he invest his capital in right coins on right time. Risks are associated with any type of investment so you have to be courageous to get good profit. Nowadays bitcoin investments are best for short term or long term.