I just got back from a couple of days in Niagara -- meeting farmers, eating very, very well, drinking even better, and eating a lot of peaches.
Ontario peach season began July 20th, and my handy new Ontario Peaches Variety/Availability Guide tells me that we're already well into group 1 of the varietals: Harrow Diamond and Springcrest, with Harrow Dawn, Early Redhaven, Garnet Beauty and Risingstar just coming on. There will be more and more right through the end of September.
But I'd suggest you get them now and keep eating. I picked some straight from the tree, where they basically exploded in my mouth and down my chin. (Juicy as all get out.)
Now, as if I haven't already been helpful enough, here are some farmer-approved peach ripening tips: Select peaches on the basis of background colour, not the reddish blush -- you want an all yellow backing, nothing with a greenish tinge. Remove peaches from container. Sort according to ripeness (read: firmness). Store ripe peaches uncovered in the fridge for up to five days. To ripen peaches quickly, store in a paper bag at room temperature. Bring peaches up to room temperature for ideal peach eating conditions. And have tons of napkins standing by.