She said that scientists all agree

but no one knows why people lose their ability to learn a new language as they age, right?

However, I heard on youtube a different philosophy stating that if an adult can spend 5 years staying in the same environment that a baby is in and focusing on learning a new language, s/he can do as well as a baby does. Do you know if there has been such an experiment carried out by patricia Kuhl or her colleagues to verify it?

From my own observation, I am more for this different voice than for the academic standard understanding -- I know it is partly because the theory shown in your video discourages idealistic second language learners like myself. :-)