I was wondering about that. I found statistics and up until 1955 or so all the girls names in the top 5 ended in -ko. That changed slowly over the next decades and by 1985 not a single name in the top 5 ended in -ko anymore.
I do think there must have been some exceptions as I've met about 20 girls named
Akiko in my life and they were all born in the 80s, so -ko names couldn't have been completely out of style at the time, I guess they just weren't used as frequently anymore.
I think
Aiko was really common in the early 2000s, I once read it was the #1 name for a while.
I really like
Taro, I know a guy named this.