I used to be able to "multitask" when I was in my early 20s and I got a lot of stuff done which resulted in my fast career progression and overall I noticed my knowledge about everything grew. The more I learned the easier it became to learn new things since pretty much everything is derived from something else, the concepts are quite similar. It doesn't take much to connect the dots.
But the "multitasking" had its peak and gradually became worse when I entered my 30s and now I'm 36 and I have to struggle to finish a book (or a course) and I hate myself for it. Whatever progress I make in one sitting that's more or less it. Every time I start reading a book, I immediately think about another book I could read. I have more kindle books, paper books and audiobooks than I will ever have time to finish and yet I can't stop myself from buying more.
It's a real struggle focusing on one thing and finishing it. I know some people prefer the freedom of doing multiple things at once but I think it's a trap and that freedom will eventually come at a price of attention disorder. The more things you do, the more things you want to do and with everything being immediately available these days, it's not that hard to get trapped in a vicious circle.
Perhaps my fault is that I used to read to complete an achievement and I did it for a very long time and somewhere along the way I forgot to read for pleasure; much like I listen to music or look at paintings.