You figure that many start to decline by 30 and you're talking big money. If you draft a young talented OT in the first round than you have 5 years at a value. That would take Tunsil to 32 and you've just spent a bankroll on him for those 5 year.
Might not be "aging veteran" but at the end of 5 year span we are now looking for someone to replace him.
So yeah, his age does have something to do with it.