While Harvey and deGrom's ages are closer to those of veterans, Harvey has the most experience of the bunch, with just 57 games started despite being in his third season of big league work. (Though he did miss all of 2014 following Tommy John surgery, so you could say it's his fourth, if you wanted.)
Before Syndergaard's most recent start on Saturday night, when he gave up five earned runs in four innings against the Rays, all three of the starters' ERA+ were 135 or higher.