I read on Machon Moreshes Ashkenaz's forums Wedding Minhagim that it is the German custom not to wear a kittel or sargenes under the chuppah. I know that it is worn on Rosh Hashannah and Yom Kippur, as well as by the shliach tzibbur on Hoshanna Rabbah; some also wear it at other times, but those three are the only ones specified by MMA, which does not say what the first occasion for wear is. Does anyone know when it is first worn?
Based on my knowledge - having grown up in the Yekkish Kehilla of Johannesburg and Strasbourg:
Yekkes do not wear a Kittel/Sargenes during their first year of marriage.
Some Yekkes do not wear a Kittel/Sargenes on Rosh Hashono at all, others wear it during the day-time services.
On Yom Kippour all Yekkes seem to wear their Kittel/Sargenes ; after their first year of marriage.
As a side point, in a typical Yekkish Kehilla, all males are expected to wear a white Käppchen - or a least a white Yarmulke - during the Rosh Hashono day services and the entire Yom Kippour services. (Most men will also wear a white tie.)