I don't think he is retiring exactly. Doesn't he want to go home and play for his hometown club? Whatever he does, he will be stepping down and winding down towards retirement.
He's essentially trying to go out at the top and there's a lot to be said for that. I still miss playing football but what I did was recreational; he's doing it day in day out with an intensity that must be wearing on both mind and body.
That said, watching him at the weekend, his level was such that he looked to have more to offer than just this season. I do think his consistency has fallen off a bit though and maybe he is feeling that. Regardless, his performance on Sunday was a delight: a combination of wonderful skill, incisive vision and dogged determination.
He's an exceptional player and I hope City can add a Champions League medal to his glittering collection before he leaves.