So why did they supposedly offer 28 year old Karlsson and Duchene 8 year deals?
These people need lifeguards in the shower.
Melnyk interviews are always a game of telephone. He seems to either repeat half of what has been said to him by his hockey ops guys, or off putting interpretations of it.
I would guess that he was told by Dorion that if they extend Karl, Duchene, Stone, they'd get more for them in a trade down the line, so that it was worth pursuing. That goes hand in hand with the rumours (from multiple sources) that the Senators being unwilling to include an 8 year NMC with Stone was a major factor in the contract not being successfully negotiated.
The Senators probably hoped that 3-4 years from now, if needed, they'd have an out to move Stone while he was still young and productive. It also coincided with something else Melnyk hinted at, which was if they signed all these guys, they wouldn't have money for all the other young "superstars" they have coming up. Depending on how bridge deals shake out, giving Stone a 4 year NMC coincides pretty well with when the Senators would have to start handing out big money to Chabot, Tkachuk, White, Brown, Gustavsson, 2020 4th overall or better pick, and Batherson. Karlsson said it himself, he felt if he re-signed, they were just going to trade him anyways.
So he's not really saying we can't sign these guys 8 years because they'll be too old, I think he's trying to repeat that they can't be locked in to those contracts without an out because they'd want to have the option to trade Stone or Karlsson to clear money before those 8 years are up and before they are too old.