Consider $\mathbb R^d\times \mathbb R^m$ with the group structure of a $2$-step Carnot Lie group and natural parabolic dilations. The maximal operator originally introduced by Nevo and Thangavelu in the setting of the Heisenberg groups is generated by (noncommutative) convolution associated with measures on spheres or generalized spheres in $\mathbb R^d$. We discuss a number of approaches that have been taken to prove $L^p$ boundedness and then talk about recent work with Jaehyeon Ryu in which we drop the nondegeneracy condition in the known results on Métivier groups. The new results have the sharp $L^p$ boundedness range for all two step Carnot groups with $d\ge 3$.