MagicMick seems to be the only one saying assesments are valid for 12 month.
I applied for the second officer position back in 2013 in which I completed the Maths and Verbal tests. I later got a call offering me an interview for the apprentice scheme. All info was taken from the SO appliction
I was unsuccesful and have now re applied this time around. The only test I had active was the OPI, which I have never seen before.
The wage for the apprentice year was 18/19k I believe. Can't quite remember. Then onto 26k I think once an SO.