Switch hitters always face the pitcher from the other side, and pitchers are usually better against hitters of the same handedness.
Range declines first, usually beginning around age 30, and accelerating in the mid 30s. A high training budget and good makeup can arrest decline a bit, but you will still see a knock. Speed follows range quickly, then power. Green's range is already poor, and you are seeing about 9 minus plays a season because of it. His makeup is not stellar, but with a good training budget I would expect to see at least three points lost from range by his age 33 season, which would be his walk year if you sign him to the max extension next season. Whether that is too much decline for you, I don't know, but you might expect a few more minus plays a season from him. Contact, eye and splits tend to hold longer, and signing him through his age 33 season you probably won't see much loss in power either. As a player extending during arb he should be reasonably priced, probably somewhere between $7.5 and $9 million per season (do you remember what he asked for an extension during this arb period?), and with his batting ability I would be comfortable signing him to at least four seasons (age 32), maybe five.