A 7 to 8 year deal for Bo would take him through his age 34 or 35 season. Not ideal but certainly not as reckless as other deals like locking up Bogaerts until he's 41.
So with that said, I would not mind if the team paid market value for the main stretch of the contract and then tacked on extra years at a discount to bring down the AAV. They did this with Vlad whose market rate was something like 9 for 450, but we tacked on 5 more years at 10 mil a year to get that AAV into a reasonable spot.
So say Bo wants 7 years at 200 million. Maybe he would go for 10 years at 220 million? That drops the AAV from 28.6 to 22 million, which would be great but the downside is that it carries him through his age 37 season when he's going to be ass.
So yeah, it could make the Vlad/Bo years painful toward the end, but given that we are a tax team, lowering the AAV can really add up over time. Plus, I was a fan from 1994-2014 so I can handle some lean years so long as we hang on to our stars. Seeing Halladay being claimed by the Phillies still pisses me off to this day.
Tl;DR Give Bo a 10 year contract!