Why was the time frame compressed in Breathe?

The 2017 film Breathe is a biographical film about Robin Cavendish, the longest lived responaut (one who is permanently dependent on a ventilator to breathe) in Britain, dying at the age of 64 in 1994. In the film, while they don't specify a specific year for the ending scene of the film, the character of Jonathan, his son, is clearly not in his mid-30s, as was his age at the time of the actual Robin Cavendish's death, and the film credits credit the actor as Jonathan in his 20s. Since the real Jonathan Cavendish helped direct the film, it seems like this would have to have been an intentional choice. Was this shortened timeline to reduce the amount of age makeup necessary for Andrew Garfield and Claire Foy? To avoid having to show the intervening years that had less drama? Just an artistic choice?