OPPORTUNITY DOES not wait for the ready. This is true of any profession, but especially professional football, where factors both physiological and market reduce the measure of careers to something resembling dog years. I suppose most of us learned this in the not-so-distant past. It was only 15 years ago that a forlorn third-year quarterback stood amidst a squall of confetti and watched the Rams celebrate a Super Bowl berth that, minutes earlier, the Eagles had been 52 yards away from securing for themselves. I remember sitting in the press box of what was then called the Dome at America's Center and thinking that this was only the beginning for Donovan McNabb.