Ah, My Hero Lady Tsunade!

is episode 237 of the Naruto: Shippūden anime.

Summary
After Rock Lee falls into a river during their training, Tenten has a flashback of her youth, while waiting for him to surface. When she was a child, she had dreamed of becoming a strong kunoichi like her heroine: Tsunade, and thanks to Guy's guidance she initially began her path towards becoming a legendary medical-nin. However during her training trying to heal a fish, but she failed. So she attempts to sign a contract to summon a creature like Tsunade's famed slugs, but without success because of the quarrel with Ningame, Guy's summon. After many failures, Guy notes that she had a talent for Space–Time Ninjutsu and began honing her unique fighting style. After that she realised that she was a weapons specialist and vowed that instead of becoming just like Tsunade, she would still become a legendary kunoichi.

Trivia
It is revealed in the episode that, despite what certain Naruto fanfictions show, even if you're a ninja, you still have to be of age to drink and gamble.