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  The two heavyweights will fight for the IBF title and vacant WBA belt in front of 90,000 fans at Wembley on Saturday.
  Joshua, 27, is undefeated in 18 fights since turning professional, while 41-year-old Klitschko had his first defeat in 11 years against Tyson Fury in 2015.
  "Klitschko doesn't have the legs, the power that he used to," said Lewis.
  "He has a chink in his armour after getting beat by Tyson Fury. Anthony Joshua is now taking that challenge, going after the man."
  Joshua himself asked the question in the build-up to Saturday's fight of whether "Father Time has caught up with the former champ?".
  But Lewis, who like Joshua won a super-heavyweight Olympic gold medal, says the Ukrainian's age is not the only reason he fancies the British fighter's chances.
  "Now is the perfect time for him," the 51-year-old told BBC Radio 5 live.
  "I believe Joshua is more focused, more aimed. Does he want to be undisputed champion? Absolutely."
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target: Anthony Joshua's world title bout with Wladimir Klitschko comes at the "perfect time", says former undisputed heavyweight champion Lennox Lewis.