  We test the impact of gravitational lensing on the lifetime estimates of
seven high-redshift quasars at redshift $z\gtrsim6$. The targeted quasars are
identified by their small observed proximity zone sizes, which indicate
extremely short quasar lifetimes $(t_Q\lesssim10^5 \text{ yrs})$. However,
these estimates of quasar lifetimes rely on the assumption that the observed
luminosities of the quasars are intrinsic and not magnified by gravitational
lensing, which would bias the lifetime estimates towards younger ages. In order
to test possible effects of gravitational lensing, we obtain high-resolution
images of the seven quasars with the {\em Hubble Space Telescope (HST)} and
look for signs of strong lensing. We do not find any evidence of strong
lensing, i.e., all quasars are well-described by point sources, and no
foreground lensing galaxy is detected. We estimate that the strong lensing
probabilities for these quasars are extremely small $(\sim1.4\times10^{-5})$,
and show that weak lensing changes the estimated quasar lifetimes by only
$\lesssim0.2$ dex. We thus confirm that the short lifetimes of these quasars
are intrinsic. The existence of young quasars indicates a high obscured
fraction, radiatively inefficient accretion, and/or flickering light curves for
high-redshift quasars. We further discuss the impact of lensing magnification
on measurements of black hole masses and Eddington ratios of quasars.
