you have a point when it comes to positions, although 2 is more than enough tbh, unless he is DMR/MR/AMR .. my back 4 always have double position CB/DMC or RB/CB .. so i always have my options .. so it never worth it to me to have those 3 positions together.. i bought a scout and was only CB, but rest of my players were dual positions at the back so never really needed him to play somewhere else .. so if i don't need him play somewhere else, it is a pointless for me if he play 3 positions, especially when you can buy many good 18 yo with dual positions
regarding the age, a scout will last 2 seasons unless you PT him .. so will not matter whether he is 24 or 22, he will be in the same development range