How did 2nd Century BC Romans become senators?

Question

Were they born into the role or did they get elected, etc.???

Answer 1

The answer is both, although once a member of your family had become a senator, it made it much easier for another family member to also become one.

The senators formed the upper class of Roman society. The "senatorial class" included all men who served in the Senate, and by extension their families. This class was dominated by the nobles (nobiles), families whose ancestors included at least one consul (earlier the qualification had been a curule magistracy, i.e. curule aedile and up). The first man in his family to be elected consul, thus qualifying his family for noble status, was called a “new man” (novus homo). Senators had to prove that they had property worth at least 1,000,000 sesterces; there was no salary attached to service in the Senate, and senators were prohibited from engaging personally in nonagricultural business, trade or public contracts. Men of the senatorial class wore the tunic with broad stripes (laticlavi).

Answer 2

The role of the senate and senators in Rome changed through the centuries. Essentially, senators were "conscripted" (we would say "drafted") to serve as advisors to the king. This changed under the republic.

The Roman Senate and Senators According to Livy
From N.S. Gill,

"Ancient Roman senators (from the Latin for 'old man' senex) were originally advisors to the kings from patrician (noble) families. Later, members of the equites (wealthy, non-patrician) were drafted into the Roman Senate. Together these senators were called 'conscript fathers' (patres conscripti). [Note: the military 'draft' is referred to as 'conscription'.] Romans became eligible to become senators by serving as magistrates. Membership in the Senate was for life, although senators could be ousted by the censors for immorality.
In his Roman History (Ab Urbe Condita), Livy shows how the role of the Senate and its composition changed during the early years of Rome. ...

(There are other explanations for the first senators, including their selection by the Roman people.) Romulus called them 'fathers' (patres): 1. [Romulus] created one hundred senators, either because that number was sufficient, or because there were only one hundred who could be so elected. Anyhow they were called fathers, by way of respect, and their descendants patricians. "

Answer 3

They were at first born into then. Then a limited number of them were chosen from among the lower classes to represent their interests. (tribunes)

They had a formal job heirarchy. You had to hold certain jobs and be of a certain age before you could reach the next job level.

Answer 4

A good example was Marcus Porcius Cato the elder. Read his life by Plutarch.