Learning as a kid is really over rated. Many people talk about children’s brain plasticity as an argument for learning as a child but I seriously believe that learning as an adult has many advantages.
One such advantage is conscious study. I’ve noticed in my time teaching English to Japanese kids that their ability to pick up the finer points of English is hampered by a lack of conscious practice.
As with most things, English has lots of unintuitive or nuanced elements which aren’t self evident. For example, the difference between the ‘th’ in ‘thank you’ and ‘that’ is whether the vocal chords are engaged in making the sound.
I’ve heard kids produce all kinds of variations of voiced and unvoiced sounds, labiodental fricatives and dental fricatives in an effort to find the ‘th’ sound in either of these words. Few of them get it purely through immersion and many struggle to produce it without specific instructions.
Children can also be exposed to some degree of deliberate study/practice but it’s no surprise that with a longer attention span and greater access to resources that adults can cover more ground, at least in my experience.
All it takes is an article or two and a few minutes of practice and I’ve found it surprisingly simple to get non-native adult speakers of English to pronounce many ‘difficult’ sounds accurately in isolation. Once you’ve corrected the misconception (in this case, how ‘th’ sounds in various words) adults can also develop an intuition for these sorts of things.
It’s never too late to learn and your advantages don’t wear out after childhood. Keep at it.