You don't need domain expertise to endeavour into something. As a matter of fact, disrupters often come from outside those industries and that's precisely why the disrupt the industry: because they don't have the bad habits from having the expertise in the affected industry.
What you do need is the discipline to execute. This discipline doesn't have anything to do with age or experience, is a related with the personality of the entrepreneur. That said, experience (age wise) and knowledge, never hurts to have.
Best of lucks!