Age discrepancy

The activity depicted in this telemovie took place somewhere around 1936, at which time Edward would have been about 42, as he was born in 1894. Why choose an actor at the age of 28 to play the part?

At least with Wallis, the age was about right, as Wallis was born in about 1895 and Joely Richardson would have been about 40 when she played the part.

The result comes across as Wallis being much older than Edward, which simply was not the case.