Just point out your dad's hypocrisy. I mean there's times when people play video games way too excessively, and it's like it's controlling their lives. For example, I have friends who literally spend about every waking minute of the day playing games. That's not good. But, if you're spending a reasonable amount of time playing games and it's not interrupting other things, who cares.
Adults lately, I see spending inordinate amount of times playing video games. My mom never really gave me crap for playing video games, thank God, but when I was a kid, she'd spend easily 5 hours at a time playing solitaire on the computer. So, she's bored with the solitaire now, and used to spend like that same amount of time on bubble popping puzzle games or something. Now my mom's latest obsession is Evony, the Civilization knockoff. She has like 10 cities at the same time going, and really besides when she does medical record reading work (that's her job, work from home like that) she spends most of her day playing it.
Just ignore your dad. Seriously. Older adults from what I've seen get way more addicted to games than kids usually do.