Average ages of some idol groups

Average ages of some idol groups. I can't vouch for the accuracy of this list, but it seems reasonable, and I find it pretty interesting,  I'll trust the maker's efforts and translate it:

average age     group

27.3     Denpagumi Inc.でんぱ組.inc (6 members)
27.0     Perfume (3 members)
23.3     Berryz Koubou工房 (7 members)
22.0     ℃-ute (5)
21.6     E-girls (19)
21.0     Idoling アイドリング (21)
21.4     Momoiro Clover ももいろクローバーZ (5)
20.5     Death Rabbitsデスラビッツ (4)
20.5     AKB48 (32)
20.1     Nogizaka乃木坂46 (35)
19.0     Babyraids ベイビーレイズ (5)
18.1     Fairies (7)
17.9     Keyakizaka欅坂46 (20)
17.3     Morning Musume '16 モーニング娘。'16 (12)
17.3     Shiritsu Ebisu Chuugaku 私立恵比寿中学 (8)
17.3     BABYMETAL (3 members)
12.6     Sakura Gakuen さくら学院 (12 members)


Note that Keyakizaka46 is listed as only 21 members, presumably excluding Neru as a member of Hiragana Keyaki.

Commenters were struck by how young the average age of Babymetal is. If you calculated  by month born rather than just year born, it would be a bit higher (17.7). But that's close enough, and gives me confidence in the maker's method.