A codger is an endearing old guy. Your tiny, eccentric grandfather might be thought of as a codger by his neighbors.
You can use codger to talk about a funny old man, especially if you're fond of him. While it's common for codger to be a term of affection, it may be seen as derogatory by the person labeled that way, so it's best to use it cautiously. You might laugh with your siblings about the codger next door, but you should probably do it quietly. The word stems from cadger, which is a now-obsolete word for "beggar."