Len Smith of Yorkshire, England, has never planned to retire.For the past 30 years, he's maintained a thriving online freelance copywriting business that brings in about $120,000 each year.In fact, he even wrote a book on the subject, "How To Be A Copywriter And Earn Money From Home," which he adapted into a course through online education site Udemy about three years ago."I was contacted by Udemy out of the blue," Smith remembers. "They said they liked the course, and thought it was ideal for their marketplace."While now 71-year-old Smith wasn't initially thrilled to put together a course ' after all, he had a full-time job to hold down ' he realized its benefits when he fell ill and wasn't able to meet his copywriting deadlines for months at a time."I went through a terrible period until July where I could do very little writing, and suddenly realized I had money coming in from Udemy, so why didn't I run down the copywriting side and focus on the courses'" Smith says.By that time, he had written a handful of courses on topics including copywriting, SEO, punctuation, and conducting presentations, which were bringing in $2,000 to $4,000 a month. "I looked at it and was like, 'This money is coming in, and I'm doing absolutely nothing whatsoever!'" Smith exclaims.So he started putting some effort into marketing his courses. This summer, he sent an email to his existing students alerting them to his other Udemy courses, and found his side income rose to $5,500 to $6,500. In November, he earned $8,500 from the courses. "There was a real change there because I realized what an opportunity it was," Smith explains.Overall, Smith's courses have reached nearly 30,000 individual students, some of whom have taken more than one of his courses.When he's creating a course, he estimates that he spends 30 to 40 hours a week, but once the course is live, maintaining and marketing it takes only about 10 hours a week.He has scaled his copywriting business back to his two main clients, both of whom give him enough notice that he's able to plan assignments in advance.In fact, he just put up his ninth course, "Copywriting Secrets ' How To Write Copy That Sells," and it brought in nearly $3,000 in two days."I think that the courses that do well ' although that's relative depending on your topic ' all show some real social proof that the creator has seen it and done it themselves, rather than being trainers talking about a subject," he says.Smith points out that because much of Udemy's audience is young men looking to make a quick fortune as web or app developers, his successful courses probably won't make an appearance in the site's most popular anytime soon.However, he does have some advice for people who want to create an income stream from their own expertise via Udemy: Join Udemy Studio, the Facebook group administrated by the company that's open to anyone interested in creating a course, and take Udemy's free tutorial on building a successful course."I could never live the lifestyle that my wife and I enjoy without working," says Smith. "We live a lavish lifestyle, so I always intended to work forever, as it were. I'm retired in terms of my age, but it's very fun ' I enjoy doing this."SEE ALSO:How This 25-Year-Old Made $66,000 In A Month By Teaching An Online CourseJoin the conversation about this story Click here to read full news..