Certainly NOT, in fact most German customers you’ll see at the clubs are usually larger, older guys. If being naked bothers you then it’s common to use two towels, one wrapped around your waist and one over your shoulders. Rest assured you’ll fit in and no one will notice you anyway. People don’t stare much as this is nothing new to them. At first you might feel a little odd wearing only a couple of towels and some slippers, but after your first session you’ll be convinced it’s all worth it.