Yes, it is more than possible for an adult to have ADD. I know this from personal experience. I was diagnosed at the age of 15 as having ADD, and I'm 30 today.
If you have trouble concentrating on one thing for a period of time, you just might have ADD. I have a lot of trouble trying to focus still till this day.
I have been given all kinds of cocktails of drugs. My favorite is when i went to a the #1 clinic in USA, well at the time, and they asked me if I ever heard of "METH" and then they went on to tell me that Adderall was basically prescription Crystal Meth.
I tried the drug thing...and one point they had me popping 3 or 4 pills. And when taken all together are suppose to make me normal.
No, they made me awake....always having the feeling that I needed to piss. Oh, and the fact I couldn't eat because speed is a food depressant just sucked. I said screw this and sold the drugs to my curious friends.
Today, I do not take any medication and will tell you there are other ways to cope with these problems. Don't fall in the trap of meds.
People with ADD are often smarter and learn faster then others.
This was my problem. I guess when you have a 140+ IQ, it's very hard stay focused when your mind is so brilliant. This is true for most people who have ADD. There just to smart for their own good.
So, if you are diagnosed with ADD just say NO to all those horrible drugs......and if you really need something to bring you back to earth....just smoke some weed....it's from the earth.