My 12 year old son wants to improve his 800m and 1500m pbs. He's running fit but has just started on the track and has time to do 2-3 training sessions per week. Can anyone advise how long for example it might take to get an 800m pb down from 2min 38 secs to 2 min 30secs? Or a 1500m pb down from 5m18s to 5mins? I'm wondering if this takes a few weeks or a few months of focussed training? Many thanks for any thoughts, appreciating this is not an exact science!