The Question of Enlistment

I have had a reply from The Great War Forum with a possible dates for Jonathan's enlistment, but first I'd like to mention that during the early part of 1916 Parliament was discussing conscription for men as opposed to volunteering.
January or May 1916 is the date for that new law, The Military Service Act 1916 and stated this

Every British male subject who
- on 15 August 1915 was ordinarily resident in Great Britain and who had attained the age of 19 but was not yet 41 and
- on 2 November 1915 was unmarried or a widower without dependent children

To further read this new law go here - http://www.1914-1918.net/msa1916.html

So back to the reply from Andy Pay -

Looking at a few men with similar numbers that were in either the 7th, 8th or 9th RB, the closest one that I could find was only a couple of numbers after your relations we find that the attestment was early December 1915 (12/12/15) and then sent straight to the Army Reserve, mobilised in June 1916 and after training posted to the relevant battalion with quite a few of these being killed in action at the Battle of Arras in either April or May 1917.

Ok, so this is my very rough working out of dates - (please correct me)
Jonathan had his first child in 1913, then my Grandfather in early January 1916, going back 9 months would take us to early April 1915, he may of enlisted voluntarily in December 1915 and as above states then going to a training camp (see here for training - http://www.1914-1918.net/training.htm ) I wonder if the above reads after enlisting he was told to mobilise in June of 1916, which meant he had from December 12th 1915 till June 1916 at home. Come June 1916 the training continued for a few months (maybe 5 months?) untill he was sent to France.

A story doing the rounds in the family thinks he may of been in France for only 5 months. That would make it December 1916 in France, I guess he would of had training in France before being sent to the front, and skimming the diarys I see early 1917 the battalion are doing a lot of training.

Your thoughts?