  Increasing evidence suggests that He II proximity profiles in the quasar
spectra at z ~ 3 - 4 are sensitive probes of quasar ages. But the development
of their H I counterparts is difficult to trace and remains poorly constrained.
We compare the UV spectra of 15 He II quasars with their high-resolution
optical counterparts and find a significant correlation between the sizes of He
II and H I proximity zones. The luminous quasar HE2347-4342 displays a null
proximity zone in both He II and H I, suggesting that it is extremely young
(age < 0.2 Myr). Three other quasars also display small proximity zones for He
II and H I. There is no evidence that a H I ionization zone expands
considerably faster than its He II counterpart. The results suggest that the
expansion of quasar ionizing fronts may be noticeably slower than the speed of
light, and raise the possibility of distinguishing young and old quasars from
the sizes of their H I proximity zones.
