Sure, risk it when you're young, but don't think that the older you get the less risks you should take. It's just the opposite. The "old dogs, new tricks" adage is a fallacy designed to keep people in line. Don't believe it! Take risks when you're young, when you're middle-aged, and when you're old!
I agree that if you don't have other factors like kids or a mortgage, there's no reason you should take less risk, aside from the natural how-many-earning-years-left risk profile that people often follow with investments (ie. Most people shouldn't "risk it all" two years before they retire, etc.)