Learn English – Difference between “estimation” and “evaluation”

Aged means that the person or people you are referring to is/are of the given age. It's always referring to someone. In this case what follows the verb to be is an adjectival phrase acting as a complement, and since it is talking about the subject, it's specifically called a subjective complement. But the important thing is that the main form of [aged 12] is that of an adjectival phrase.

The boy is aged 11.
I'm aged 20.

Aged can usually be replaced with of age:

The boy is of age 11.
I'm of age 20.

Now, when talking about age alone, age is a noun and [age 11] is a noun phrase. In the case of your examples, [college aged students] and [college age students] represent two different cases of noun modification.

[College aged] is clearly an adjectival phrase.
[College age] is clearly a noun phrase.

In the first case, [[college aged] students] you are modifying a noun [students] with an adjective, which is correct.

In the second case, [[college age] students] you are modifying a noun [students] with another noun, which is also correct.

Summing up: for the specific case of the question, it would be the same and would have almost the same exact effect to use either [college age students] or [college aged students].

Affiliation is generally a closer and more formal connection than association is. I think affiliation is used more in the professional world than outside. There is a connotation of exclusivity with affiliation. If someone is affiliated with, say, one university, he or she is probably not affiliated with other schools.

(Also, regarding preposition choice, note that in the U.S. you would usually say or write that you are affiliated with or associated with a group of people.)