I guess I will do you a service and educate you on this.
It will be highly unlikely that the A's bring Inoa up until he is 20 years old, and even then it is more likely he is brought up when he is 21.
So here is how the clock starts on free agency.
3-years of service in MLB and you are arbitration eligible.
6-years on a roster until you are free agency eligible.
This means Inoa at the earliest because a free agent when he is 27 more likely when he is 28. The A's will get at least 6-years of Major league service out of him. The 25-28 year old period will likely be the prime of his career, sure you can throw out guys like Clemens, Randy Johnson but those guys are the exceptions not the rule.
Alternatively, the A's could do something similar to what they did with Rich Harden. Sign him to a contract extension during his 3rd year to avoid arbitration. It would not be difficult to lock him up at a 4-year contract at that time, which could give the A's 7 years of his services.
I guess there really is no consensus on when pitchers seem to decline, but most studies really put that from about 28 on that pitchers start to decline.
http://www.baseballthinkfactory.org/...rs_to_decline/