it 's as if allen , at 66 , has stopped challenging himself . 
(ROOT (S (NP (PRP it)) (VP (VBZ 's) (SBAR (IN as) (IN if) (S (NP (NNP allen)) (, ,) (PP (IN at) (NP (CD 66))) (, ,) (VP (VBZ has) (VP (VBN stopped) (S (VP (VBG challenging) (NP (PRP himself))))))))) (. .)))
(ROOT (S (NP (PRP )) (VP (VBZ ) (SBAR (IN ) (IN ) (S (NP (NNP )) (, ) (PP (IN ) (NP (CD ))) (, ) (VP (VBZ ) (VP (VBN ) (S (VP (VBG ) (NP (PRP ))))))))) (. )))