at seventy, he should have much grayer hair
If season four opens in 1928, Harry Selfridge would be seventy! Jeremy Piven seems to be playing a dashing 45 year old.
Why should we assume Mr Selfridge should be grey because you are?
It also doesn't seem like enough time has past for Mr Grove's oldest child with his second wife to be 18. That's right? He didn't have any kids with his first wife right?