「好きな人は結構好きだと思います」は英語で「People who like it are really into it.」と言います。「People who like it really like it.」も言えますが、「like」が二回言っていますので、あまり自然だと感じないと思うので「really into it」(ハマる)を使えばいいと思います。「結構好き」のニュアンスも入っています。
最近の若者はまだアイドルが好きですか?
好きな人は結構好きだと思います。
Do young people these days still like idols?
People who like them are really into them.
I think that the people who like it really like it a lot
people who like (something)
(そのものが)好きな人
to really like (something) a lot
が結構好き
I think that the people who like it really like it a lot
好きな人は結構好きだと思います
話す時にreallyを強調しますね。I think that the people who like it REALLY like itやI think that the people who like it really really like itなど
ご参考になれば幸いです。