Non-competes cannot be forever because it would in essence end your career and it would be unconstitutional.  Oftentimes, such contracts are limited in duration and mileage.  Any contract that is against public policy or too restrictive would be or could be voidable.  

Many states do not recognize non-competes as valid and other states have limited their enforeceability.  The less restrictive, the more enforceable.  Hawaii Revised Statutes Section 480-4 is the section covering non-competes. Here is the link; you will see the "reasonable" standard used in your state: http://www.capitol.hawaii.gov/hrscurrent/Vol11_Ch0476-0490/HRS0480/HRS_0480-0004.htm