Also, a lot of the public schools had active OTC units before WW1, so could provide young officers without too much extra training. Public Schools and the Great War by Anthony Selson and David Walsh is an interesting book.
Speaking as a childless person, I don't actually see the problem with being one of the first groups. I'm in my 50s so it wouldn't affect me directly, and I already work in a defence-related role, so it would just make work a lot busier. But we have a lot of ex-forces employees, so that would have an impact.
I think fitness levels might be challenging for conscription. I suppose a lot of young people are very into gym-goung, but others are absolutely not. WW1 also highlighted issues with fitness levels, malnutrition, under-nutrition and related health issues.