Hi there.
DP started his training in august (as Peachy said).
Many things change force to force but I can tell you what Thames Valley do.
DP applied then waited about 5 months to get through the papersift (the hardest part by all accounts) then another 3 months before assessment centre, then he had two physical/medical exams, and background checks. He was given his appointed station just under a year of applying and that is very quick.
His wage is the same as here but as he is TVP he gets £2k pa extra, in the met they get £4k pa extra.
Training isn't residential any more unless you live further away from your training centre than would travel to your allocated station, then you will have a choice between being paid travel expenses or living in force housing.
For training at TVP they do 6 weeks at college, 3 weeks PDU (working alongside a constable tutor at a local station), 4 weeks college, 4 weeks PDU, 4 weeks college, 4 weeks PDU then fit for independent patrol.
DP's shifts are either 8-6, 10-8, 12-8, 4pm-midnight or 8pm-4am. He gets one full weekend in three off, does one night shift, and a full weekend of days. He gets a full three rest days after one late (4-12) and two night (8pm-4am) shifts. This won't change much when he is off PDU. He is given his shifts 3 months in advance. Apparently they are quite flexible if time off is needed as long as you give enough notice and don't take the piss.
IMO, night shifts aren't too bad, I quite like them and as DP is in at about 5am he sleeps til about 1/2ish and then we have the day together.
There is absolutely no guarantee that you will finish at the time you're meant to though. DP's first late shift was meant to finish at midnight, so I waited up for him. I went to bed at 3am, he got in at 4:30 but that can't be helped, he had to book in some firearms which means a specialist unit had to be there.
Holidays, well, as has already been said, you can book the time off but if something happens they can cancel it with hardly any notice.
I find it easier with his shifts than I did when he was on a 9-5 because he normally has 1-2 days a week off, or he is home for the morning so he can do more in the day than he could previously.
Being a mature probationer wouldn't be an issue at all afaic. In DP's intake around 50% of them are older people with parents, the other 50% are young and single.
Family wise it can be fab, I mean you won't get job security like it elsewhere, and there are a large number of insurance plans taken out incase of any problems, if DP gets injured he can get two years off full pay for example. Pension is good, wage is quite good, DP's fed rep is supposed to be really helpful in absolutely anything that you may need help with. In short, the police look after their own, but you have to work the hours and do the job.
If you can work round the shifts with a long enough notice period and have people that can step in on emergency then I would say it won't be a problem, but he has to get in first!