1) Well clearly he popped in OD last week so yes meaning he can still be improved. The real question is if you think that it's worth it to spend time training him given how much training slows down at that age. I don't know exactly how much training slows with age but my experience with trying to train a 24 year old in passing last season is that you're looking at a 24 year old training at about 60% of the efficiency of an 18 year old. (I could be way, way off with this number and I would love for someone to correct me with exact numbers since this is more of a guess based on a single experience than anything else)
2) You pick a skill to train in one drop down box and in the other drop down box you select the positions you want to train and you pick one of the two position options which differ for each type of training.