I agree my favorite riding temperatures are between 55 and 70. But, I love fall the most, and I like winter, too, because I can do different sports. Fall and winter are what they are supposed to be, but, many times, spring isn't. So in March, when I am going out on my first rides, I don't like it, even though it is no colder than it was in November!
But, I think Oak is right. When you slowly acclimate yourself to the heat, it is easier. I did that last summer, since it was so hot. I ride on days I never would have before, now, but I get out early, and often if it's in the nineties, my rides are slower and in a particularly shady location. You just have to be careful and learn what you need for hydration. And I second the water bottle for dousing yourself. I always have one bottle of plain water.