I posted in another thread about the language ability I USED to have, as a teenager. I learned French and German in high school, picked up a lot of Dutch, taught myself Spanish, and minored in Portuguese at university. And I had a near fluent level in most of these languages.
Then something strange happened by the time I was 19 or so. I rapidly lost ability to speak, and retain, languages. I think it was maybe because I spread myself too thin, trying to master so many languages, maybe I burnt myself out? Perhaps it might have been better to focus on cultivating one, or at the most two languages? By that time I'd tried to learn Italian as well, but just couldn't pick it up.
After I graduated from university (age 21) I tried to teach myself Russian and Chinese but got nowhere. Yes, they are more challenging languages for an English speaker, but I think it was more because I'd lost patience and more importantly concentration at becoming proficient in languages. As sometimes happens with Aspies, some interests pass by, and so it proved for me with language proficiency.
Notice I say language proficiency rather than languages as an interest. I'm still interested in languages but nowadays have a virtually complete lack of concentration in learning them. My interest in languages nowadays, is in the English language and the etymologies of its words. This is an area where I've been able to concentrate and retain better.
Because of an interest in etymology of the English language, I'm now more interested in old and ancient languages. If I was to learn new languages now I'd be far more interested in learning Latin, Greek, Hebrew or anything ancient like that.