I agree with what the guys wrote above.
I have a friend who is a 40 year old masters racer. He used to train over 20 hours/week as a sprinter (lifting, road rides, ergo workouts, etc...) He had good results. Then he had a kid. Training time was cut significantly. His results were similarly good. He remarked to me that he didn't need as much training volume as he (and his coach) thought.
Also, understand that your competitors also have jobs, kids, lives, etc... So they can't train like a care-free 22 year old "full-time athlete", either. So, the playing field is sort of level.
Don't feel guilty about backing-off or missing workouts. We ain't gettin' paid for this
Working out while tired actually does more harm than good. You probably won't get what you need out of the current workout and you will definitely hurt your recovery and the next workout. So, if the workout feels really bad, then just quit and call it a day and move on.
Also, workouts feeling abnormally bad may also be an early sign if the cold/flu. I've heard athletes say that they know when they are about to get sick a day or two before it hits because they are tired during their workouts.