Today almost anyone can make a few bucks on the Internet, even a little kid. There are all kinds of micro job sites with simple tasks that pay micro workers. Anyone can work there and the tasks are easy to accomplish. But to make a steady income, they have to be mature persons.
If they want to develop a real freelance career, they have to have knowledge. So it does not matter how old they were when they started. Only their skills, experience, responsibility and other aspects of their characters make it possible now.