Cats are grazers by nature, and will eat little often, the behaviour you describe certainly seems normal to me. One point you mention, is the fact he always goes to his bowl after being out in the garden, when he is in the garden he will be watching the wildlife, this by nature will make him think of food, usually at this point wild cats will kill and eat or store their prey, but our lazy by nature domestic felines will supress this urge by eating a bit from the bowl. I would be more concerned if he wasnt eating. I would though (if his appetite is huge) let him graze on a more lower fat dry food, this is usually branded as "senior" by the more known brands, just make sure plenty of water is at hand.