No matter your age, it is never too late to learn a new language. Research and anecdotal evidence have both proven that adults can acquire languages similarly to how children do it. In fact, adults aquire languages faster than babies. The advantage of being an adult is that we can use various tools and techniques to speed up the process, such as the AJATT method, which can typically help one become fluent in a language within just 2 years. This is a far cry from a typical 4-year-old child who, despite having been exposed to language input constantly, still doesn't sound very good and still makes some mistakes.