Do you have a pic of the second one? Both the same breed, I assume? I'm definitely leaning toward pullet - about 10-12 weeks old, my guess.
From what I've learned, it's not about the size of the comb alone, it's about development of the wattles also, and color of each. Cockerels' turn red earlier, pullets not until they are closer to laying. I have hens that everyone thinks are roosters due to their wattles and combs, they're the same sizes as the roos'. They did develop slower than the roos though.
That was also my guess on breed, I was just looking back at pics of my red sex links from several years ago. Definitely a pullet if that's the case. Great starter birds, be prepared for a ton of eggs! I got 1 a day for all but maybe a month a year out of mine, they are laying machines. And usually very friendly.