As someone who had a gameboy growing up, and now a child, I had to quickly do some math to console myself that I'm not yet "Grandfather" age. This is simply a (now) old man who had fun toys as a (normal age) adult.
But the (horrifying) maths checks out: say he got the Gameboy at the age of 12 when it launched in 1989, had a first child at twenty in 1997, that child has a child of its own also at the age of twenty in 2017, grandchild aged six or seven now excited to find granddad's Gameboy. Twenty is merely youngish for a first child, not the stuff of shotgun-wedding backblocks.
When I was 17 I had a job at Software Etc (a forerunner of Gamestop), and person checking out asked if I had any kids. I was kind of bewildered and said "I think I'm a little young for that" and she sort of shakes her finger in front of me, "oh no you're not honey"
I've been thinking about that ever since, marking various dates in my life where I could take this theoretical kid out for a beer, etc. If my child's child had made a similar… um… life decision… I could be a great-grandfather in two years.
I'm similarly haunted by the question of an avuncular Anglo-Indian office manager some thirty years ago who upon learning that I had no kids exclaimed "How do you know that you're not just shooting blanks?!" I've wondered ever since how is have explained to that putative first-born that really they were just the pipe-cleaning debugging trial run, just making sure that the baby-batter cannon didn't need a rebore before settling down to a proper production run. (I'm sure that he'd have regarded my eventual brood of two as being confirmation of my lack of earnestness...a dilettante of the dong department)