The Chidah writes (in his sefer Arvei Nachal) that there is a known remez in the Torah to getting married at 18. The Passuk says “Vehu Naarah Bivsuleah Yikach”. Vehu is gimatria 18. But he then continues and says something very relevant to this conversation.
He says there;s another hint to 18 in the passuk. The last letters of the words “naarah bivsulaeah yikach” also are gimatria 18. Says the Chidah: “Why did the torah hint to age 18 at the END of the words? And he answers that there will be a time, at the end of generations before Moshiach, when people will say that “Ben 18 L’Chupa” was only in “the olden days”, that it doesn’t apply today. Therefore The Torah hinted to 18 at the END of the words, to tell us that 18 applies even today!
The Steipler as well as the Chazon Ish also held that 18 applies even nowadays.