The closest we have to an official altitude limit for model aviation (in the USA) is a "strong memo"
An Advisory Circular is advice, not regulation. Disregarding that advice and causing a problem can be looked at as criminal negligence though...
There are regulations as to what type aircraft need what level of communication with other aircraft and air traffic control based on where the aircraft is operating. This can get very complicated.
No comment on other countries' rules... They don't have to resemble US rules, though there are a lot of duplications worldwide, especially for commercial aviation.