I have been asked to reply.
A Government commissioned report by the Transport Research Laboratory published in October 1998, investigated the effects of the UK adopting single/double summertime (i.e. GMT + one hour in the winter, from October to March, and GMT + two hours in the summer, from March to October) thereby making the evenings lighter throughout the year. It concluded that, there could be a net saving of over 400 people killed or seriously injured per year in Great Britain, including over 100 deaths.
The 1998 research did not identify casualty savings by age.