Neuroscientists believe we have about 100 to 500 trillion individual synapses firing in our adult brains. So although our desire to continually stuff our minds may be earnest, brain capacity is finite--about one to ten terabytes, and it's estimated that the average person's vocabulary treads water well under 100,000 words.
When I was growing up, road trips meant I was frequently captive audience to certain kinds of niche talk radio programs—which were bad enough without those commercial breaks in which the hosts proselytized for ointments, powders, or self-help devices. One product in particular haunted me: it was some kind of vocabulary building system, and there was Rush Limbaugh intoning from a script that a person's vocabulary stops growing at the age of 25.
At the time, 25 seemed like such a geriatric age that it seemed feasible and somehow appropriate that that language acquisition should cease. It also seemed to me that there was no way that at 25 there'd be any words I'd have left to master! This was at the height of my draconian spelling bee training, so a little arrogance should be forgiven.
So here I am, fully two years past the so-called vocab rigor mortis age, and I'm still learning new words! Most of them seem to be unnecessarily impenetrable (and thus more fun) synonyms for words I'll probably keep using (e.g. "prestidigitation"). And I could fill a month's worth of posts on how many words I spent many happy years mispronouncing or worrying I was mispronouncing--an invocation of "palimpsest" was heavy on the "limp" until I finally learned either way (i.e. "pal" or "limp") was okay, and my favorite grammar school vocab years was always "deSULtory." I find it either takes a good friend or a bad job interview to correct such things. But back to acquisition: any other brave flossers want to out themselves on words they've learned post-25? And if you're under 25, a) how cute! and b) just kidding, please regale us with any $5 words you've picked up lately.