Sashihara Rino provides her opinions about the shelf life of idols, and a recent 2ch threads follows up with their responses about the “appropriate” age range of idols.

First off, the three appropriate age ranges of idols, according to Sashihara Rino:

“16 years old is young”

“18 years old is middle aged”

“22 years old is elderly!”

In a sense, I can see where she’s going here, but the most notable exception I can recall is Shinoda Mariko, who didn’t enter AKB until she was 19 years old, and she was 27 years old when she graduated a few years back.  Kojima Haruna, also still a member of AKB, is also 27 years old.

One might be hard pressed to call her elderly, but denizens of 2ch are quick to point out the exceptions as well:

• Shibata, Takayanagi, Matsumura are all zombies! (柴田とか高柳とか松村はゾンビかよ)
• This is the first time Sasshi has started saying random crap. (指原の適当発言は今に始まったことじゃない)
• Nyan and Ume-chan are living off of mist.. (にゃんさんとか梅ちゃんは霞を食べて生きてるレベル)
• I guess I’ll join the senate at 24 years old. (24歳になると元老院入りします)
• For idols, this is really normal (アイドルってそういうもんでっせ普通)
• Kojimaki just turned 18 yesterday. Middle aged, huh… (こじまこ(昨日で18)で中堅なのか)
• So, I guess this is how it goes. 1st – 7th gen: fossils. 9th-11th gen: veterans. 12th-14th gen: middle aged. 15th gen, 1-2nd gen draft: young. (もうこうなるのかな。1期-7期が化石。9期-11期がベテラン。12期-14期が中堅。15期・ドラフト1期・ドラフト2期が若手)
• But it seems that most don’t get really popular until their 20’s (でもAKBは20歳越えてから人気がついてくる例が多い)
• Is this an elderly gathering? (老人会かな？)

With regard to the last statement, one commentator makes note of the ages of ranked members, as below:

• 1位 22歳
• 2位 23歳
• 3位 21歳
• 4位 18歳
• 5位 21歳
• 6位 24歳
• 7位 21歳
• 8位 18歳
• 9位 22歳
• 10位 23歳
• 11位 19歳
• 12位 17歳
• 13位 24歳
• 14位 25歳
• 15位 18歳
• 16位 23歳

Doing some math, the average age of the senbatsu members is 21.2 years old.  Gathering old oldies indeed!!

Sauce: http://chikakb.ldblog.jp/archives/44985663.html