The surest, safest thing to do is to arb him this season, and then sign him for his age 28-32 seasons next season. Regardless of how many years he is asking for, he will accept 5 seasons at the same annual salary.
The controlling attributes are probably patience and OVR; better players seem to hit the open market more. 70 patience seems unlikely to keep him around any longer than he has to; so take the 6 years you can get.
Finally, the loyalty tiebreaker is a pretty highly-rated one, so you are pretty likely to be able to sign him as a free agent to a max contract for his age 33-37 years, if you so desire.