A very important topic: as "startupermen," 17–18 year-olds who don't yet understand what business is are doing startups.
A startup isn't a trend — it's a business
The word "startup" has become a trend, and many young people start one without learning the fundamentals of business. But a startup is first of all a business: demand, economics, sales, and market logic. A "startup" built without understanding these often burns money and time.
Conclusion
Before doing a startup, you need to understand business itself: is there demand in the market, who pays, what are the economics. It's not the idea but business logic that keeps a startup alive.