The idiom thin as a rake means extremely skinny or slender, which is how the man is described in the context.
Consider the statement "An older man, extremely skinny or slender, with curls for hair and a face as lined as rotten fruit.". Based on this "An older man, thin as a rake, with curls for hair and a face as lined as rotten fruit." a true statement? Yes, no, or I don't know?