Exactly. 28-32 years of age is prime time in the NBA.
Curry is a better example. He's 30 years old and averages 34 minutes a game. He's only played in 625 games so far. Does anyone truly believe he'll make it to 1000 games with his current injury history. My point is that Bjelica's usage rate is nowhere near those of Lebron or Curry, and he hasn't played in nearly as many games. So he's a much younger 30 than Curry is. I wouldn't be too worried about Bjelica's age.
I once had a sports medicine doctor tell me that the human body is made up of multiple hinges. Knee's, elbows, ankles, etc. And like any mechanical device, they wear out over time. The human body does a great job of replenishing itself, and the individual can help by eating right and taking the right supplements. But there is an inevitable end. The question is, when?
That said, I like Bjelica and think he would be a nice additiion to the team. If you dig through his stat history, he's more productive the more minutes he plays. And as previously stated, when Butler went down with an injury he was inserted into the starting lineup at the SF position, and he played quite well. He's a better than average defender, even at SF, but as it's also been stated, he could defend the 4 and play the 3 on offense switching roles with either Bagley or Giles. Not saying he's the be all end all, but that you need players like him on your bench. Hope they sign him!