Several resource allocation settings involve agents with unequal entitlements represented by weights. We analyze weighted fair division from an asymptotic perspective: if $m$ items are divided among $n$ agents whose utilities are independently sampled from a probability distribution, when is it likely that a fair allocation exist? We show that if the ratio between the weights is bounded, a weighted envy-free allocation exists with high probability provided that $m = Ω(n\log n/\log\log n)$, generalizing a prior unweighted result. For weighted proportionality, we establish a sharp threshold of $m = n/(1-μ)$ for the transition from non-existence to existence, where $μ\in (0,1)$ denotes the mean of the distribution. In addition, we prove that for two agents, a weighted envy-free (and weighted proportional) allocation is likely to exist if $m = ω(\sqrt{r})$, where $r$ denotes the ratio between the two weights.