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Due to lack of canonical information in the franchise, there is no definite answer to this question.
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The topic of this question is tentative in nature and may possibly change in the future.
The characters' exact ages haven't confirmed, though it is assumed that all the main characters are at least over 20.
Tigress is at least over 20. She became Shifu's student probably after then Tai Lung was put in jail for that long, as she states in Kung Fu Panda 2 that she used to punch ironwood trees for that long and was teenager 10 years ago as revealed in Secrets of the Scroll.
Crane is at least 26, as Po states in Secrets of the Furious Five that he was at the Lee Da Kung Fu Academy twenty years prior, and as Crane states in the episode Mama Told Me not to Kung Fu he had to wear armour until he was six years old before he worked as a janitor at the Lee Da Kung Fu Academy.