5k before 28? definitely possible. But most probably not by solid income. I'm 23 and working in the entertainment business; acting, script writing and voice acting. 5k per month is really easy if you're well known, and if your contacts get a lot of projects, especially from RTM. And if you're able to juggle your schedule, even 50k is possible.
Let's say you're a scriptwriter writing for a 26 episode drama series, the least I've heard for an episode's script is RM800. That's 20800. If you're acting on the side as a supporting cast you can get another 6000-8000.
But the downside is it's really luck. Sometimes you get jobs, sometimes you don't. Prepare your maggi. And even though you get a lot you don't have a permanent job payslip so you can't make a car loan or housing loan. Which is why many local artist start businesses. Apart from the side income they can also make their own payslip to 'pay' themselves.
Option 2;MLM.

You could also go tender hunting. A friend of mine got rich just by finding companies that supplies sand for a mega project. He got 10 cents for 1 tonne of sand supplied. The project used 80-90million tonnes of sand. Then he used the money to open a kopitiam, which was successful, earning 1.5-2k daily easily.
Qualifications for all of the above; SPM
It is definitely possible to get more than 5k from just a full-time job without part-time income b4 28.