Most young players only get a chance when senior players are out though.
He hasn't shied away from having to do that and put players out of position etc.
Agreed - No manager is going to bench a senior player just because they have signed someone young. Generally an injury or a poor run of games gives the youngster their shot. It think what you look at is, does Martinez sign folks like Hitzsleberger for depth or does he look younger and someone he can groom. To me he generally looks younger with a long range plan in mind. The two notable exceptions I think were Kone and Alcaraz and I believe they were brought in as Martinez wanted depth AND someone familiar with his style of play to ease the transition.
Lennon was someone that could provide a spark to the first team and did just that.