Roman Army before and after the Marius' Reforms

[JaM]

And that is what I wrote in posting #25 of this thread: “But what if the Romans allocated an age division for the levy to each property class, with Class I recruiting the oldest men, and Class V the youngest? In this manner, Class V, being the youngest and more fleet of foot but the poorest would be recruited to serve as velites in the army.”

then why Polybius and Livy both state that Proletarii were not allowed into Legion?  

And of course, what i wrote before, wealth and age don't necessarily mix up, just because you are poor, it doesn't automatically mean you are young, and vice versa. You could be a young (18-19) member of a wealthy family (Class I), while you could as well have 40-45 years old poor farmers that would also fit the census.

(anyway if you have some more detailed info on this, preferably exact citations of Polybius or Livy or any other ancient historian, i'd be grateful)

and one different view - technically, members of Triarii, were usually those who had their service almost up. It would make a perfect sense not use such men in the front rank and risking their lives, after all, they are those who will be able to be elected into offices as their military service is completed.