Probably. Don't know your situation, and I'm not 40 anyway, so take everything I say with a grain of salt.
One thing I've noticed, having worked for startups with older founders: when you're over 35, it's to your advantage to start a different kind of company. When you're in your early 20s, it makes sense to swing for the fences with a new consumer idea that's wildly innovative and nobody really understands. That way, your lack of experience isn't really a drawback (nobody knows what they're doing, so the fact that you don't know either isn't a significant problem) and your youthful energy lets you discover and explore the market faster than all your older competitors. Plus, much of your peer group consists of people who are open to new ideas and will be "growing into" your market. You can understand them better than older folks. And you can live on less money, which is important, because new markets usually don't involve much cash.
When you're over 35, it makes more sense to leverage your existing experience and network and go into a field close to your existing job - often, your first customer will be your last employer. Start small with something you can sell for cash, quickly, and then leverage your network to expand to other customers. You're protected from all the young tykes because you know the market and technology better than they do, and you fend off the big companies by concentrating on a niche that's unprofitable for them to devote much attention to.
This, of course, depends upon having experience and contacts to leverage. If you spent your whole career working as a janitor, it may be pretty difficult to start a company, unless you've discovered a new more efficient way to mop floors. But if you've spent your whole career as a sysadmin, it makes a lot of sense to build server administration software that does your job, only better.