Different answers can be given based on, for example: how long it's been in use/development; range of vocabulary; population of speakers; how closely it can express logic with mathematical exactness; the wealth of metaphors, or commonly known parables/stories as part of the language; the consistency of grammatical rules, and lack of exceptions; ease of learning, how long an average person takes to become fluent; simpler to read/write/speak, or the opposite, how complex it is.
The answer also depends on the user, their skills, use cases, and context. Someone may use a language in an "advanced" way, to think/express elaborate thoughts, in poetry, or in science. Another may use the same language to grunt rude and nonsensical insults.
Is a pair of pliers more advanced than a hammer? Is Picasso more advanced than Matisse? Surely a computer is more advanced than a rock, but when you need to open a coconut, the latter is a superior tool.