That's...debatable, but it has one particular clear, specific interest in normalizing reconquest of formerly-held territories, irrespective of whether it is “aggressive” or “expansionist“ in any general sense.
> Significantly less than Russia and the US.
While it has integrated as states some territories it already held in that time, the US has been anti-expansionist since 1947, voluntarily relinquishing formerly-held territories and seeking neither to acquire new ones nor to reassert sovereign control over former ones. (The US may exercise strong influence over foreign states, including many that it formerly administered as territories, and may entertain the idea of integrating existing territories as states, but territorial expansion hasn't been on the table for a while.) China, in the same time period, has launched several wars for territorial expansion.
> Wasn't their last war the annexation of Tibet in 1951?
No. Excluding internal (even arguable, like several with the ROC) wars, since 1951 they've fought in the Korean War, several wars with India, the Vietnam War, several wars against Vietnam after the Vietnam War, and some others. Against both India and Vietnam, particularly, their goals in involved territorial expansion.
That said, I believe the Soviet Union has taken quite a bit of land from China a long time ago, and although they haven't made any claim on that land yet (unlike with Taiwan, Hong Kong, and the South China Sea), I can imagine China might want it back when the time is right for it. Like a serious collapse of Russia. But I don't think they'll go to war over it.
Also, apparently there exist some Finnish imperialists who'd like to annex Karelia, and possibly some other parts of North-West Russia.