Can’t concentrate. Can you develop ADHD later in life?

So over the last few months; I’ve been having difficulty concentrating on things. When I was reading a book; it took me far longer to read as I kept going back and re-reading it as I felt I was skimming through it and not concentrating on the content. I need to re-watch YouTube videos because I feel like I didn’t absorb the content. I’m reading a new book and I feel like I’m just reading it too fast and not absorbing the message. I have two projects. One recreational and one for school and I can’t start them. I keep getting distracted and the school project requires me to read a bunch of stuff that bores me so I haven’t started it yet. It’s due in a week. I am in grad school by the way. I have severe OCD and I am heavily on meds for it. I am also almost 28 years of age. Is it possible I am developing ADHD. I would take a test to determine this but I know that when I take it; my brain will subconsciously concentrate so I can protect myself from any scrutiny.