If he could contribute well, he would have been given a decent number of minutes. But he's not getting any younger and is already at the peak of his career, so it would be wiser if the management lets him retire. Kevin Love is older than him by three years, but Kevin Love is making more contributions to his team, especially since signing with the Miami Heat.
Every player will have an end, but this kind of ending may not look good in my opinion, as it might seem like when you're at a job, and they aren't satisfied anymore, so you're advised to resign instead of being fired.
We can't conclude it yet as he still got plenty of time to make every minutes count, with this opportunty to retire his jersey it's possible just in case he send inside to play decent minutes he needs to showcase eveyrthing that left in him to make it valuable, like you said hes not getting any younger but it's the opposite.
If he got that chance to play make sure to provide some help, though he's not that very offensive but the help in giving a tough defense and grab some balls to collect for both offensive and defensive stats.