To really nail this down, think about what kind of elderly man you're talking about. Is he wise, like an old tree or an owl? Or is he slack and tired, like an old shoe?
Is his skin deeply wrinkled, like a raisin or a walnut? Or is does it have thick, deep lines like carved wood?
Is he smiling and content? Frowning and sad? Think about your character, picture him in your mind, and then think about what the picture reminds you of. Have fun with it!