Nowadays, everyone in school seems to own a smartphone.
I didn't own a smartphone until I was an adult with a job.
12 year old kids are doing things with smartphones some adults don't know how to do.
スマホを持つのは12歳からが適切だ
It is appropriate to have a smartphone
from the age of 12
今日、学校の全員がスマートフォンを
所有しているようです。
Nowadays, everyone in school seems
to own a smartphone.
仕事をする大人になるまで、
私はスマートフォンを所有していませんでした。
I didn't own a smartphone until I was an adult with a job.
12歳の子供たちは、
一部の大人は方法を知らないスマートフォンで物事をしています。
12 year old kids are doing things with smartphones
some adults don't know how to do.
I think it's appropriate for kids to have their own cell phone starting around the age of 12.
この場合、次のような言い方ができますよ。
ーI think it's appropriate for kids to have their own cell phone starting around the age of 12.
「子供たちが自分のスマホを持つのは12歳ごろが適切だと思う」
appropriate「適切な・ふさわしい」
around the age of 12 で「１２歳くらい」
ご参考まで！
アメリカ合衆国 
カナダ 
