Loggerhead sea turtles don't really care if they have algae, barnacles, etc. on their carapace. On the other hand, green sea turtles love to be clean. That's why you'll see "clean greens" because they will rub their flippers, carapaces, etc. on hard surfaces to rid themselves of epibiota. I've seen green sea turtles at cleaning stations where the fish are helping to clean the turtle. Hawksbill sea turtles will usually be quite clean, too.
It's hard to determine the age of a sea turtle, however, by weighing and measuring a turtle, a marine vet can give a pretty good estimate. Sea turtles can live 80-100 years as long as they don't get in trouble. The first picture of the turtle shows a rather large tail (cloaca) and that's how we know the turtle is a male. The cloaca is a common chamber and outlet into which intestinal, urinary and genital tracts open. All turtles have a tail, however, the female retains a short tail while the male grows a long heavy tail. Sea turtles don't start mating until they are 25-30 years old. This ol' boy has probably been mating for awhile. Nesting season in Cozumel should begin in a couple months. Nice!