I think he started to become unsettled here once the Man Utd rumours started and he then made up his mind that he should move on. Then Bayern came knocking which was ideal for him...pretty sure he has a big affection for Germany, having played there before. Bayern didn't want to renew and he reluctantly returned, thinking he'd move on in one of the next 2 transfer windows. The Jan window was a bust while waiting for the next one, he was seriously getting to grips with his LWB role and think it's here that the dial began to swing back. Then came the Scudetto. Then came Inzaghi who has really helped him enjoy the game. At this stage, he's happy to stay and commit. The problem is the offer, which I think he views as derisory. If reports are right, Brozo is getting 6m. Perisic is asking for the same and I'm sure it's negotiable...but the club is still pretty far away. I think the last figure mentioned was 4m.
As for physical decline, it's inevitable but Perisic is built different from others and I think he should fare better than most, barring injuries. Even with physical decline, his defensive abilities would still be better than most others in the game regardless of age.
The club may have a different assessment...perhaps Perisic has indicated internally that he's more inclined to leave or that he's unwilling to move much at all on his asking price.