和英辞書

大人買い

noun

(slang) Of an adult, buying (chiefly childish) things in great amounts (due to newfound purchasing power).

彼は新刊のコミックを大人買いした。

He bought all the new comics in bulk, like an adult.

意味（1）

(slang) Of an adult, buying (chiefly childish) things in great amounts (due to newfound purchasing power).

https://books.google.com/books?id=obQ7t1LsBnoC&pg=RA1-PA23&q=%22%E5%A4%A7%E4%BA%BA%E8%B2%B7%E3%81%84%22#v=onepage

https://books.google.com/books?id=obQ7t1LsBnoC&pg=RA1-PA23&q=%22%E5%A4%A7%E4%BA%BA%E8%B2%B7%E3%81%84%22#v=onepage もちろん今(いま)なら買(か)えるぞ。あの頃欲(ころほ)しかった、例(れい)のクロモリの最上機種(さいじょうきしゅ)だって、なんということはない。いわゆる「大人買(おとなが)い」ができる。

Mochiron ima nara kaeru zo. Ano koro hoshikatta, rei no kuromori no saijō kishu datte, nantoiu koto wa nai. Iwayuru “otonagai” ga dekiru.Of course, you can buy it now. That top-of-the-line chromoly model you wanted back then isn't anything big. Now you can buy all you want.