I think around the 27 age where players pass the RFA status, and teams can no longer control them they become unlikely to get a chance at an NHL job. Nothing wrong with a 24 or 25 year old prospect. they just have a short window.
http://www.merriam-webster.com/dictionary/prospect
1pros·pect noun \ˈprä-ˌspekt\
6 b: a likely candidate for a job or position
Players are no longer prospects when they either
have a NHL job, because they are no longer candidates,
or they become unlikey to get a shot at an NHL job. I would argue Knight and Wolf are probably 2 of the top 10 most likely to earn a job this year.