Joe Hart turns 30 this season - 30 million is ludicrous. He has optimistically 3 or 4 more years at the top of his game most likely as he's not a in my mind a keeper like Buffon or Cech who defy age simply because they're so astute in their positioning.
29 is quite young for a keeper, even David James was cutting it in the prem at 40
Hart probably has 5-6 years left at the top and more at a decent level