I’ve known Japanese who lived in various places for a while and picked up their accents. One guy had quite the twang. It was funny listening to him.
My 6-year-old son is worse at learning English pronunciation than my 8-year old daughter is. She’s always had a better ear.
My daughter has a friend who moved to California from London when she was 6 & her sister was 8. They are now 13 & 15 and have no detectible British accent, but both parents kept their accents.
When identifying a specific age for losing/keeping an accent, I wonder how much difference it makes when the kid first starts speaking. My kids started talking around 1-2, but I have a nephew that didn’t start talking after 4.
I grew up in Massachusetts. Age 9, I moved back to Arkansas with a strong accent. My New England accent disappeared within a couple years.
I remember being teased for my accent at school. Losing my accent was a priority.
I was born and raised in Brooklyn until age 6. At that time, I had a pretty heavy Brooklyn accent IE I’d pronounce God as Gawd and other such words. At 6, my family moved to a small town in Middle NJ and I was also sent to speech therapy as I had a speech impediment and during the course of the therapy, I lost a large chunk of my accent. My accent became a weird mix of “proper” American English and NY accent which other kids said sounded "British’ and for which I was mocked. So my accent became less and less pronounced. My family moved back to Brooklyn in 2002 and have remained so since. As I’ve gotten older I’ve made a conscious effort to reclaim my original accent. Some words and phrasings never left me. For example, I say “clicka” instead of “remote”; I say “rad-e-ate-er” instead of radiator. I say fus-trated instead of frustrated. I say “whatchmacallit” and refer to my mother as “Ma” and always have. But it’s been an effort reclaiming my original voice.