It's an argument that gets brought up a lot, especially when the people arguing are really, really attached to the previous Era.
Before platinum Era was "a thing" there was a lot of complaining about it. A LOT. With Yossi graduating, a lot of people complained she was the last Golden Age member, therefore the group was going to suck now. When Miki left, a lot of people complained that without Miki the vocals would sound horrible because the only person who could sing was Takahashi (Remember, at the time, Risa, Eri, Reina weren't front girls. Reina had lines, but she was more of a B-girl, what Eri and Risa turned into.) and this meant Koharu would get all the lines. No one was happy with Aika. Sayu wasn't even a blip on the radar. Neither was Eri. A lot of people were upset that management was leaving Morning Musume in the hands of girls who have yet to prove themselves vocally or personality wise. Sound familiar?
In 2007, the start of platinum Era, the ages were this: 14 (Aika), 15 (Koharu) 16 (Linlin) 18 (Sayumi), 18 (Reina), 19 (Risa), 19 (Eri), 19 (Junjun) 21 (Ai).
Quite a few people actually said, at the time, Platinum Era was a bit top heavy. BUT they really weren't that much older than the girls now. Haruka is 13, yeah she's pretty young but on her way to 14. Masaki, Sakura and Kanon are 14, same age as Aika was. Riho and Eripon are 15 (Koharu). Mizuki, Ayumi are 16 (Linlin). Haruna is 18 (Sayu/Reina), and Sayu is 24.
Average age of platinum Era in 2007:
15.6 17.6
Average age of Colorful Era now:
14.4515.9 (
13.515.0 without Sayu, if you must know.)
Is that THAT much of a difference? No.
I think the biggest thing that people are doing is that we aren't quite used to 9th/10th/11th gen yet, as 9th Gen is just over 2 years old. All the girls from Platinum Era who weren't 8th gen had plenty of time for us to get used to, some of those girls had been there since 2001. We don't have that luxury with Colorful Era and some people just hate that.
BTW I'm a huge opponent of putting young girls in Momusu, as most of you know. I always root for the older girls. But when I crunched the numbers for myself, I realized that these new girls aren't that far away from Platinum Era as I thought and kinda shut up about the "Platinum Era was better because they were OLDER" thing
EDIT: THe vocal argument is laughable to me, I could get into it, but it would make this post longer. Let's just say there is a lot of bias there when people argue "Platinum Era sang better than Colorful Era"... A LOT of bias.
EDIT 2: MATH CHECK, thanks guys