Joseph,
You’re comparing ending Shabbos earlier than Rabbeinu Tam, which has a source, with what you say is a strict mandate to marry at 18 even nowadays, no exceptions? You just made my point, 18 isn’t the standard in the Yeshiva world. It wasn’t in the Lithuanian yeshivos either.
You claim to live in Meah Shearim part of the year yet your posts indicate that you know nothing about living in Israel. You claim to have three wives yet your comments show that you know nothing about marriage. You make pronouncements about when bachurim should marry but it’s obvious that you know nothing about yeshivos.
edited