How to get the generative counterpart of a discriminative CNN

Say we train a (discriminative) CNN to predict age from images of faces. Is there a direct way of obtaining the homologous generative network (ie, from a scalar age to an image of a face) ? The backward pass during training should be doing something similar in order to propagate the gradients from age to the face.

There is probably no good way to do this, since it is possible to discriminate age without modeling the whole space of faces. If you also happened to have a density model of faces $$X$$ as well, perhaps you could use MCMC to sample from $$P(X|y) \propto P(y|X)P(X)$$.