and did Russia recognize Crimea as part of Ukraine between 1989 until 2014?Well ok, on that note, there's a critical difference with Crimea: it used to belong to Russia, but the Soviet Union gave it to Ukraine while both Russia and Ukraine were under the Soviet Union.
"It used to belong to us." is a slippery slope.
It allows the Koreans to reclaim Manchuria/Gando because of Goguryeo/Balhae legacy.
It allows the Outer Mongolians to reclaim Inner Mongolia because of the Yuan dynasty (or all of China for that matter).
It allows China to reclaim Vietnam because of 1,200 years of Chinese domination of Vietnam.
Just in principle, it's just bad to justify annexation because: "We used to own it (at one point in time)" because who is preventing the revival of Mongol empire or British empire?
After the dissolution of USSR, for all practical purposes, Ukraine kept Crimea while Russia kept their naval base in Crimea. The closest analogy with China would be Japan keeping Diaoyu Island, so no, I don't see this as Russian aggression at all.
Except Russia recognized Crimea as part of Ukraine between 1989 until 2014. China never recognized Diaoyutai as part of Japan between 1945 until present day.
Russia had to engineer a complex "Crimean Referendum" (vote to join Russia) to legitimize it's annexation, whereas China doesn't need to make fancy justifications, it can just point to Qing-era maps.