Get a cable tester and see what the cable type/qualtiy and signal characteristics are. Or if you're near some other equipment that is high-EM (where shielding may be needed).
There is nothing theoretical about the official numbers with a quality install:
* https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Var...
In the ISO/IEC structural cabling standard the length is strictly informative, and the length of a cable/run doesn't matter as long as the signal characteristics are good: you can have a 130m run and a tester will not pass-fail based on the length, but on the signal quality:
