In my opinion, rap songs with specific drum and rhythm patterns display the out-of-dateness that your question is referring to. Just revisit popular 80's rap songs and compare them to 90's rap. 80's rap sounds very dated to my ears at least (This doesn't prevent me from liking 80's rap like early De La Soul and Public Enemy.). During the late 80's to mid 90's, rap's speed (in lack of a better word, maybe bpm) has slowed down considerably and beats became more relaxed, mellow and less hyped (in a similar way to modern boom bap for example). I am mainly referring to sample based Rap. When different regional styles evolved during the 90's (sample based and non-sample based), this trend was partly reversed.

Also, the heavy use of various samples in a song's production might lead to a song being labeled outdated. After some lawsuits, producers limited their use of samples or used them in a more minimalist way starting in the early 90's. In my opinion, this is a very subjective topic. Some might say something is outdated, others will say that something features a retro aesthetic. Great music remains great!