Dear Marco, looking at the yearly progression of the athlete, we can see a "stagnation" during the last 4 years in 800m (an improvement between 18-22 years of 1.11 is very little) while, at the same time, his improvement in 1500m is ok (5.45). This fact means that the SPECIFIC TALENT of the athlete is not in direction of a high lactic endurance, but of "medium" lactic endurance supported by a good aerobic level. I have some doubt seeing the weight (67,6 kg seem to me too many for a runner 1.74 tall), so I suppose that he can be a "muscular" type of runner. But probably this is due also to the lack of long run. I think that, if this guy goes to long run (for example, twice a week 1 hr 20:00 progressive with last 20-30 min fast) he can lose 3 kg becoming about 64 kg heavy.
So, I suggest the following road :
1) Increase the mileage, and the number of training sessions per week. He can run an average of 160 km per week, going (one week every 3, during periods without competitions) also very close 190 km. This is a correct base for an athlete that is talented for longer distances.
2) Put him in some long competition on road (one HM in 62:30, per ex., and 1-2 times 10k under 29:00) in order to build a correct mentality for every type of event, playing down the idea of fatigue connected with distance
3) Go for long intervals on track (for ex., 2000/3000/2000/1000/1000/1000 with short recovery of 2/3 min, running at 10000m pace (about 2:52 per km, ex : 5:45 - 8:40 - 5:45 - 2:50 - 2:48 - 2:45) trying to maintain during the weeks the same speed, reducing recovery times
4) At the same time, go for "medium" intervals in sets (for example, 4 sets of 600/500/400/300m with 1:30 recovery, alternating speeds : 1:36 - 1:14 - 62 - 42 for the first and the 3rd set, 1:28 - 1:18 - 57 - 46 for the 2nd and the 4th set) using 5:00 recovery among the sets
5) And use full speed with very long recovery, for example 5 x 400 in 53 rec. 8:00, or 3 x 600 in 1:22 rec. 8:00, for increasing the LACTIC POWER, that is a very important part of training.
In this way, you can prepare the athlete for changing event in 3 years, but the first effect is THAT HE CAN IMPROVE IN 1500m and also in 800m (may be 3:36 and 1:47 ?). Remember always that training is WHAT YOU DO. Don't be afraid about distance, or about speed : is all the ingredients are present in a programme, the athlete can improve in every distance, IF IS AEROBICALLY TALENTED.