He played with injuries this season and that's fair to point at to show why he might be on the decline, his body showing affects of all the NBA games he's played. But I think that's at least debatable with the type of work ethic and conditioning he's maintained throughout his career. As far as his game, "signs of decline" have been greatly exaggerated. Come playoff time, despite playing nowhere near 100%, again he was putting up 30 point games like they were going out of business. Had no problem pushing through injuries and wear and tear of three consecutive long playoff runs to play at a very elite level. I don't think there is nearly as many "signs of decline" as some might suggest.
Again, I point out at guys like Reggie Miller and Karl Malone who were likewise religious about keeping in great shape and both playing into their mid 30s playing at an elite level. I can easily see Kobe at 35-36 still playing 35 minutes and averaging 25 ppg.