You've gotta be kidding. Think of the era in which he was President. I was in college, the internet hadn't been invented, Bill Gates was still working out of his garage and Macintosh was a kind of western raincoat. Anything he knew of any importance was obsolete inside of ten years, max. I seriously doubt that anybody in GW's administration gave him clearance above FOIA (Freedom of Information Act) that every citizen has. He might be getting raw data from his elite buddies in the CFR and T/C but that's all.
You think ex Presidents do not have access to consultants (such as Sandy Berger was for Clinton) who see (and make profits from) current US/world intelligence? As well as intelligence from the UN, French, Germans, and other agencies? Do you not think Jimmy Carter was given 20 and 30 year force projections when he was President, and updates at his request since then? The guy is getting briefed at State and probably other agencies every time he travels or returns, even if he is a traitorous antisemitic old POS. he still gets treated with the decorum and perks of a former President even if he doesn't return the honor.
Regardless of the accuracy of his statement it can be assumed by many in the US and outside the US, that he has inside information and street cred.
So again I say- who is he sending this message to, about Israeli nuc arsenal? And why? A warning to Iran? Apologia for Syria?