Being able to talk comfortably is just a guideline. How fast you can go and still have a conversation is just an outcome of how fit you are. It also indicates how warmed up you are. Anytime you head off on a ride, you have to factor in some warmup time. In running, you warm up to the point where you've got your "second wind." It's not so dramatic in cycling. If you just start slow and let the speed come up by itself, you barely notice that you've crossed this threshold.

Also, the fitter or stronger you are as a cyclist, the longer it's going to take you to warm up. More muscle mass takes longer to warm up. I've known track sprinters that take about an hour to warm up. Back when I was racing, I'd do a 30-km warmup prior to a 15-km criterium!

Luis