Is there any situation where a male is not permitted to wear a gartel in prayer. I was told by a rabbi of a popular movement that I should never wear a gartel. I was not given a reason and wondered was it because I was not a married person? Was I incomplete in my yiddishkeit at some level?
I have never come across a reason for which or a situation in which a person would not be permitted to wear a gartel. The idea of a gartel is to form an additional separation between the lower half of the body and the upper half, as preparation for prayer. This is not a halachic requirement, because the belt a person wears, or the pants themselves, already form the basic separation required. The custom has been adopted primarily by Chassidim, and anybody who wishes to practice it may do so freely.
One interesting halachic aspect of the gartel is the question of wearing it in the public domain on Shabbos. This question is discussed by a number of autohrities; see Piskei Teshuvos, Shabbos, 301:14.