1. I agree with Steve Davis that a pool champion would most likely be a snooker champion if started out early with snooker.
2. I think it would be really hard to excel in snooker after 30 because the brain does not form myelin as well as we get older and societal pressures as an adult hinder learning. However I do sincerely believe in my heart that any top pool player if given a solid year or two of deeply immersive snooker training would emerge as one of the top 100 snooker players in the world. I would consider that a professional success IF one could make it to the top 100.
Corey has NO CHANCE doing it as a part time activity. Maybe no chance as a full time one either.
Regarding your earlier comment about Hendry retiring and so on, with any activity it gets tougher each year to be motivated for it. It's not just the eyesight, it's the desire. Once you have reached the pinnacle then there is no where else to go. It becomes a drudgery to go to event after event year after year and you simply don't want the pressure of being the one expected to win all the time.
I can agree that age slows some people down but at snooker or pool if there is no physical handicap then I think it's lack of desire and motivation more than anything else that leads to poorer performances.
Look at Efren winning so many championships after 40.
From Wikipedia:
The 2012 Betfred.com World Snooker Championship professional ranking snooker tournament took place from 21 April to 7 May 2012 at the Crucible Theatre in Sheffield, England. It was the 75th edition of the event,[1] and the last ranking event of the 2011/2012 season.[2]
Ronnie O'Sullivan won his fourth world title by defeating Ali Carter 18–11 in the final. John Higgins, the defending champion,[3] lost 4–13 to Stephen Hendry in the second round.[4] Aged 36, and just 55 days older than Dennis Taylor when winning the title in 1985, O'Sullivan became the oldest world champion since 45-year-old Ray Reardon in 1978.[5]
On the opening day of the televised stage Hendry made the 88th official maximum break, his third at the Crucible and the 11th of his career.[6] He announced his retirement from professional snooker following his loss to Stephen Maguire in the quarter-finals.[7]
Stephen Hendry made a maximum, his 88th. Ray Reardon won his last championship at 45 and now Ronnie has won at 36 and again at 37.
I see no reason why top snooker players can't stay at the top well beyond 40 if they are fit and still desire to play.