If you check the PRT instruction (start at BUPERS web site and search) I think you'll find the 12:00 etc. equates to the good low for the age group. I was an old dog when I got there, and I wondered if it was 12:00 for all the guys, or Good Low for your age group. Since I couldn't get a straight answer, I trained to the 12:00 standard. I usually swim the PRT, so it sucked, but I made it. After I finished, the NASC Chief supervising us looked at my scores and my age and said, "Sir, it didn't really matter anyway, you had another XX seconds or so because Good Low for your age is 12:XX." I thought that was great timing. I also did six extra situps that didn't count because they forgot how old I was and hollered at me to keep going after I'd maxed out for my age group. Oh well, I passed and it was one less thing to worry about. Don't worry about which standard to use, just make sure you can make Good Low for 25 and under, and you'll be set. And yes, the chip trail is slow, especially when the chips are gone and it's mostly sand, but it's easy on the knees, and you're in the shade!