When I was a kid, I really wanted an older brother.
質問ありがとうございます。
逆だと、自然に聞こえませんよ。
❶When I was a kid, I really wanted an older brother.
(小さい時、お兄ちゃんがめっちゃ欲しかった)。
こう言えますよ、
When I was a kid, I really wanted an older brother because I wanted somebody to play with.
(小さい時、お兄ちゃんがめっちゃ欲しかった,なぜなら遊び相手が欲しかったから)。
参加になれば嬉しいです!