Instant Teen Vol 2

Instant Teen: Just Add Nuts by Haruka Fukushima. A Romance manga rated Teen, published in English by Tokyopop.

Fifth-grader Natsumi Kawashima can't wait to grow up, so when she eats some mysterious pink-tinted nuts created by scientist Dr. Yunosuke Morinomiya, she wakes up in the body of a young woman. Now she has to juggle unexpected romantic attention while keeping her real age a secret. A sweet, silly shojo comedy.