I don’t know the answer to your question about the ligs in young men compared to older men but you should also know if you don’t already know that you can also get gains from enlarging (lengthing and wideining) the tunica to make real penis gains by litterly deforming your penis little by little to grow the whole shaft. The tunica/shaft gains are much harder to get then lig gains but I believe they may be more permanent and after a while it seems to get big length gains in PE you need to start targeting the tunica/shaft eventually for length when your LOT reachs close to 6:00. That is what has happend in my case, I gained lots from lig gains and now I’m gaining from tunica gains.
Also a little tip I have for you for making lig gains (I don’t know if this will help you, me being age 24). Try to do a lot of manual stretches when you have lots of time in one session at certain angles below your LOT to hit the ligs better, try to do a good amount of V-Stretchs and Inverted V-Stretchs (you get better at these the more you practice them) also. With the V-Stretchs pull your dick straight out in front of you while standing or sitting and when it is taut and not elastic press down with your other hands thumb right near the base on the middle of the shaft. You should feel a guitar like string thing, which is the tunica septum we believe, but if you use your thumb and feel around the shaft near the base you can locate the ligs and press down right there with a good amount of pressure while holding your dick streatched out with your other hand in a overhand OK grip taut. This will put intense tension at the base of your dick where the ligs are and fatigue that area quicker. You want to aim for fatigue/soreness at the base of your dick where the ligs are where your pubes start. When you feel this fatigue/soreness after sessions you know you are putting in good work. Later it gets harder and harder to fatigue/get sore in this area and that is the sign it is time to fatigue/get sore all over the shaft/tunica for furthur gains.
Good luck, hope this helps…