This is mostly about everyday life - and not so much about gaming:
I don't have it, but my ex-GF had it and was diagnosed near the end of our relationship.
We lived together for 2 years.
She wasn't into gaming, but I tried introducing her to a few games a couple of times. She would start out being interested, but couldn't maintain interest.
She did love games like Plants versus Zombies and Farmville - and would play them in a way I might call obsessive, but who am I to judge that, eh?
Anyway, in terms of everyday life - it definitely affected her in a big way, and I would often suggest to her if it might be ADHD - but she wouldn't accept that and dismissed the notion.
She had a very hard time just sitting down and relaxing, and her biggest problem was finishing non-physical tasks that she knew had to be finished - like with her school projects. To me, it seemed that the fact that something HAD to be finished put an enormous amount of pressure on her, and she did everything she could to distract herself from doing it, because the thought of it having to be done - and her having to sit down and do the work just made her crazy. Big problem was that this distraction resulted in even more pressure, because time was always running out for her.
This made her very hard to be around when she had an important project, because she was so stressed - and nothing I said or didn't say seemed to help her or make her happy. I tried not saying anything at all - and that made it worse, because then I wasn't supporting her enough when she just needed to vent about it.
Anyway, she just couldn't make herself sit down and finish the damned homework, so she distracted herself. She would clean the house constantly - or she would go shopping. Sometimes, she would shop 4-5 times per day, which was something I'd never seen before. Personally, I loathe shopping and will keep that down to a minimum.
Needless to say, we had a lot of conflicts in the house - as I'm the exact opposite of someone with ADHD. I prefer to relax - and most tasks are chores to be done with me. So, because I hate having chores - I just do them immediately with very high efficiency - and I would NEVER do them as a distraction. This I do so I can focus on whatever it is I WANT to do. I'm not necessarily a messy person - though I'm sure many would think so - but I was absolutely NOT as "clean" as she would have wanted me to be, and she would often complain I didn't help out with the cleaning enough. I tried my best to contribute - but I also made it clear that it would only work if we made specific agreements about it, as cleaning "just because" would never, ever, be something I wanted to do.
The ONE thing we could do together with great success was to watch movies - and have dinner afterwards. I couldn't quite figure that out - because that meant sitting down and relaxing - but eventually I "got it". It was her way of letting go of her thoughts and just passively engage them in something pleasant. She's the only girl I've been with who loved movies more than I did - and we, literally, saw at least one new movie or the occasional episode of a TV show every day. We went to the movies very often - and sometimes several times per week, which was also kinda nice, because I hardly ever went to the movies otherwise.
I would have thought playing games could work in a similar way for her, but apparently she couldn't enjoy them because of the strain or pressure she felt when being challenged. This was something she told me often, but I didn't understand until she was diagnosed. So, to her, the worst part was definitely the pressure of having to focus her thoughts and accomplishing a challenging task. It scared her a lot.
This makes the condition resemble OCD in a way, though I realise it's a separate condition. But OCD is an anxiety disorder - and I've been suffering from anxiety for many years in the past, and I've learned to control it with quite a bit of success. But the fear is the thing - and it seems to lie at the heart of almost every kind of mental suffering there is.
