Multi-vendor marketplaces, like ThemeForest, can be very successful. Chose a niche and create a vendor website for it. Your marketplace could be anything, from a platform for local artists to sell their work on, to an online digital product store. Once set up, invite people in that industry to sell their products on your site. You take a percentage of their profits when items sell.
Invest in housing. Research the housing markets of various cities. Consider the pros and cons of each area. Decide whether you want to purchase single-family homes or a rental property. Consider putting your money in a real estate investment group to increase your ability to invest in high-profile properties. Some banks may balk at giving a 14 years old a mortgage.
No matter what method you select for generating your online income, there's one very important thing to understand. Today, across this globe, with its 7+ billion inhabitants, there are two recurring things that people are looking for more of. Either people want more time or they want more money. The truth? Time is far more valuable than money. You can't recreate time. Once it's spent, it's gone forever. Not money.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.