  In many growing networks, the age of the nodes plays an important role in
deciding the attachment probability of the incoming nodes. For example, in a
citation network, very old papers are seldom cited while recent papers are
usually cited with high frequency. We study actual citation networks to find
out the distribution $T(t)$ of $t$, the time interval between the published and
the cited paper. For different sets of data we find a universal behaviour:
$T(t) \sim t^{-0.9}$ for $t \leq t_c$ and $T(t) \sim t^{-2}$ for $t>t_c$ where
$t_c \sim O(10)$.
