Yekkes historically wear the tallet gadol from the time of bar mitzvah, which the Chofetz Chaim believed was correct.
RebDoniel:- Actually scroll back 1 decade earlier, as Jekkes usually commence wearing a Tallis Godol from about age 3.
Of-course, as you RebDoniel so rightly said, waiting until marriage is not Halocho, and does not have sufficient grounding; i.e. It has no grounding.
This fallacy is based on 2 Pesukim in Parshas Ki-Setze:- 1) Gedilim Ta’aseh Loch etc., immediately followed by the Posuuk of 2) Ki Yikach Ish Isho etc.
The only problem with this ungrounded Limud is, that the verse to wear a Tallis comes before the Possuk of a marriage, so waiting until after the marriage for a Tallis is taking these 2 Pesukim in the wrong order.
Tragically we see bachelors in their 60’s & 70’s who apart from tragically having missed out on the Mitzvos of marriage & procreation, also have missed out on the Mitzwah of Tallis Godol.