Chasidim go out at 17. So do Yidden in Eretz Yisroel. And they live in the same generation as we do.
Where have the Gedolim today said not to get married at 18? I don’t know any consensus of Litvish Gedolim advocating anything like that.
And, no, just because most Litvaks don’t get married at 18 doesn’t mean the Gedolim approve. They’re not protesting can simply mean they feel that, even though they should get married then, their protests will fall on deaf ears.