Too ambitious?

Tuesday, as I was chatting with the man who was fitting me for shoes, I watched as his face morphed into a fatherly look of concern. He learned I've been running a little under a year, have completed a half marathon and am now in training for a full. "You're certainly ambitious," he said -- and it obviously wasn't meant as a compliment.

I admit I've been a bit freaked out since then. Am I rushing this? He seemed slightly relieved when I shared that I'm using the John Bingham/Jenny Hadfield plan and merely want to cross the finish line. 

That conversation changed my fear from "can I really do this?" to "SHOULD I really do this?" Am I making a mistake? Am I setting myself up for injury or a hatred of running? 

I don't have immediate plans to give up. I'm enjoying training again too much to let one man dictate what I should be doing. But there is that slight seed of doubt, so I'm curious what others think.