I think age and quality aren't the only factors and agree one strategy for a competitive team is advance the players who are consistent performers in their roles.

2 lowest quality players on my team are doing best this season, despite age difference.
Click image for larger version. 

Name:	Screenshot_2016-12-03-13-30-31.jpg 
Views:	216 
Size:	88.8 KB 
ID:	74138
Click image for larger version. 

Name:	Screenshot_2016-12-03-13-30-19.jpg 
Views:	217 
Size:	90.1 KB 
ID:	74139