Would it be wrong for an umarried male to wear a Kittel at Yom Kippur? I see that the Mishna Berurah holds by one who waits to wear a Talit until they are married that it suprises him that one should "sit by and not fulfill the Mitzva of Tzitzit until one is married." But since a Kittel is more custom than Halacha would the same apply to it or not?

Although it is customary to wear a Kittel after getting married, I can imagine an unmarried man who is in a community with married couples feeling out of place without a Kittel. In such a situation it would be a resonable practice. However, I'd stay away from it if 1. it might lead someone to make the mistake that the man is married, or 2. it would reflect on other unmarried men. In all situations of public customs I think it is important to consult the local Rabbi. Certainly, causing someone offence or discomfort is an important consideration, and should prevent one from taking on customs which are not the norm.