Also, here is another scenario.
Tanjiro: I had a dad until I was 11???
(Rokuta was probably 4-5 as he was still small, and Tanjiro is 13 at the beginning of the show and Nezuko is 12 at the beginning of the show. Nezuko said that Rokuta had been really lonely since their dad died, so Rokuta had been alive by then. So Tanjiro had to be 11-12 when his dad died. They never specified Tanjiro's age when they showed us the bear incident, which happened 10 days before Tanjuro(Tanjiro's dad) died. But that's just my speculations.)
