If you are around 18, then you can get many jobs online. Constant-Content.com is a place where you can sell your well-written articles, start your own blog and monetize it. You can then try for AssociatedContent.com. You may design webs and sell them through oDesk. You can do WordPress theme management any design logos for small publishers and new brands. And surveys are also there.
Actually, if you can practise your single talent and utilize it, then no one will stop you making hundreds per month. My only tip would be to focus on only ONE SKILL, not many.