Constantly getting punctures. What's going on?

My dad has ridden his bike for over a year without a single puncture. But during last month he's got at least 10. He's a weekend rider so it's literally every other ride with a puncture.

I'm suspecting it's not just a roadside waste. Tho I've never ridden tubes and don't know what else it can be. I struggle to make him get his butt of the seat on curbs and uneven road. Might it be the cause?

We checked tires and rims and didn't find any sharp corners or protruding elements.

I can't see him losing wholehearted passion to cycling. I'd appreciate any help or advice.

Thanks in advance

Just to make it clear, tubeless is our very last solution.