AKB48 in end of 2011 year:
16 years old - 3 girls (Iwasa Misaki, Maeda Ami, Oku Manami)
17 years old - 4 girls (Oota Aika, Fujie Reina, Komori Mika, Watanabe Mayu)
18 years old - 7 girls (Kikuchi Ayaka, Nakatsuka Tomomi, Uchida Mayumi, Chikano Rina, Ishida Haruka, Miyazaki Miho, Sato Sumire)
19 years old - 7 girls (Nakagawa Haruka, Sashihara Rino, Minegishi Minami, Nito Moeno, Tanabe Miku, Yokoyama Yui, Hirajima Natsumi)
20 years old - 14 girls (Maeda Atsuko, Nakaya Sayaka, Ooya Shizuka, Takahashi Minami, Takajyo Aki, Itano Tomomi, Nonaka Misato, Yonezawa Rumi, Kashiwagi Yuki, Kasai Tomomi, Kitahara Rie, Kobayashi Kana, Masuda Yuka, Suzuki Mariya)
21 years old - 7 girls (Katayama Haruka, Nakata Chisato, Matsubara Natsumi, Matsui Sakiko, Miyazawa Sae, Sato Amina, Sato Natsuki)
22 years old - 2 girls (Kuramochi Asuka, Umeda Ayaka)
23 years old - 3 girls (Kojima Haruna, Akimoto Sayaka, Oshima Yuko)
25 years old - 1 girls (Shinoda Mariko)
average ~ 19.6 years old,
average ~ Team A - 20.0 years old,
average ~ Team K - 19.8 years old,
average ~ Team B - 18.9 years old,
7 girls become underage (only seven!),
7 girls will up to next lvl (underage->18 age).