You can go in deeply enough that you won't forget it even if you pick it up later in your life, but the trouble is you cannot know whether (or not yet) you have

You can go in deeply enough that you won't forget it even if you pick it up later in your life, but the trouble is you cannot know whether (or not yet) you have reached that level. If you were to pursue that as a personal project, spending a few months or one full year abroad to fully immerse and then following up back home with some routine of combined reading of books in the language and occasional meetup group to have some occasional practice/use is what I would recommend. BTW, Spanish and Italian are similar enough that there could be confusion in the learner's brain (happened to me - after two years of Spanish in school, self study of Italian from six audio tapes failed because for each word, the Spanish version was promptly recalled instead of the newly acquired Italian one). IMHO, it's worth it, and from what I read in the UK interest in foreign languages is declining (and it corresponds with personal experience, when I studied a bit of French and Russian, the French course had no Brits in it, and the Russian course just one, everyone else was a foreigner). As a linguist I may be biased, of course, but I would encourage you to pursue at least one language other than English more deeply (instead of, say, dabbling in three superficially), because it opens up a new horizon being able to navigate a culture without translator and reading its literature in the original. There are certain words, phrases and sayings in each language that when you "get" them you feel like "I no other language could one say this better!", whether it's Danish, English, Spanish, German or Latin. One of my Ph.D. advisers was British and the other one U.S.-American, and I won't forget PS: Is there a link without paywall to the original article?