Why does my accent sound like a teenager/younger person from the country I'm trying to learn, and not an adult?

This has happened to me with Spanish, French, German, Italian, Russian, Japanese, Korean... Every single time I try to speak a different accent, I sound like a younger person from that country. I cannot get rid of my "baby talk" accent (and I'm a 39 year old male), which is really bad for me because I work as a voice actor for animated shows (and I'm sure it would be a real problem if I were an actor).<br><br>Has anyone here ever encountered this problem? I've asked around for advice, and people say "watch shows from the country, listen to their accent/way of speaking" or "listen to how they pronounce things", but I've done that for years, and it hasn't really helped.<br><br>So, is there anything else I can do to get rid of this problem? If so, what? Or should I just give up trying to be a voice actor for other countries, and just stick to my own?