Exactly right! I also think that the relative ease with which the ageing system can show when it is about to possibly affect players is a major pro. If your main star is getting closer to his 4th or 5th advance then it may be time to seriously consider a replacement if an ageing roll cuts him down. And with only 1 roll it is an obstacle that can be met and forgotten at each advance. Any system of time or injuries will create a constant uncertainty as to who will remain a viable team player, beyond the already present threat of onfield damage.Ageing players with no skills just because the system is called "ageing" is just foolish. Change the name, not the system.
I voted Skill gained, as the current system is a very good starting point. Change the name (and the reasoning) to EGO, that is where the player gets a big head and, stops working out (-1ST), or decides s/he doesn't need this poncy armour anymore (-1AV), or that he has a publicity event (NG), etc.
That said, as Zombie suggested earlier, this is about the concept more so then the specifics of the system. I think a tweaking of the 'ageing' rules is better then a complete scraping in favour of something new which may not be much better received and be looked to be changed in another year. I would not be against a change of the ageing results table in particular, but I think the rolls to see if you do age, under the current system, are the best bet. It allows unlimited freedom to the coach (within other boundaries of course) to build his/her team to the level they feel comfortable with, or at least that they can maintain.