Over the years, in working with people and their dogs, I've seen a huge range in abilities. Some people, with no experience whatsoever, seem to be "naturals" that have instinctively good timing with their dogs. They manage to mark the behavior they mean to and deliver the reward in position, as I encourage them to do. Others, after weeks of practice, still struggle a bit with their timing and seem to mark late or accidentally deliver a reward for something other than what they intend. The important thing that I've learned, is that dogs are forgiving, and as long as the human is committed and builds a good relationship with their dog, the behaviors they desire will come along in time. Sure its easier (and certainly faster!) if your timing is excellent, but virtually everyone who has or wants a dog can become a "good enough" trainer to get what they want out of their dog if they are willing to learn.
This video brings a smile to my face every time I watch it. Its my two year old nephew playing with, and training quite well, his beloved dog. If a two year old can do it, you can too!