Results of an experimental study of monolayer and bi-layer graphene, electronic stopping power for low keV protons are presented. Energy loss of protons as a function of ion velocity shows an unexpectedly high value as compared with measurements in bulk amorphous carbon. Furthermore, we observe an apparent velocity threshold around 0.1 a.u., already observed in insulators and in previous work for protons interacting with multilayer layer graphene. Enhancement of energy loss and threshold suggest low dimensionality effects which can be due to possible extraordinary features of carbon allotropes and the interlayer electron density distribution.