I think what people who talk about "old languages" use to determine a language's age is something like "what's the earliest date an ancestor of this language wa

I think what people who talk about "old languages" use to determine a language's age is something like "what's the earliest date an ancestor of this language was used in writing" or "how long has this area been inhabited by populations genetically similar to modern speakers of this language". Personally, I think most languages are old, except for constructed languages like Toki Pona that have only existed for a short time.