Peaches like a nice, warm sun bath to ripen. If you’ve come home from the market/farm stand/orchard with some peaches or nectarines that were picked a bit early, just stick them in a paper bag, loosely roll down the top, and leave them on your kitchen counter for a couple of days. The ripening fruit gives off ethylene gas. Trapping the gas in the bag concentrates the ripening effect, speeding up the process naturally. Using a paper bag allows just enough air movement to prevent moldy fruit.
Ripe peaches are fragrant, heavier than they look, and give just a little when you squeeze them. They are usually best eaten over the sink, with a napkin close by to wipe the juice that drips to your elbow.
The same trick works for plums, nectarines, avocados, kiwis, mangos, and pears.