Honest way (no cheats): study, study, study! Make sure to have all the needed skill points and then do research, go to class, write your term paper, and do assignments until your GPA meter is above the bar and white remember to go to the final exam on time.
Honest way (with minor cheat): Turn on boolProp and drag your sim's skill meter to the needed amount. Then, turn motive decay off and hit maxMotives. Pick up a book and start researching; you don't even have to go to class! (not sure about the importance of the term paper) I do this all the time and my sims end up with so much free time on their hands they just streak for three days straight. Go to the final exam on time for that perfect 4.0 GPA and that coveted Dean's List money.
Dis-honest way (no cheats): Find the professor of your major and get them inside your dorm. Sleep with them (I have only heard about this method so I've got nothing else to say).
Dis-honest way (major cheat): I'll get back to you on this. Uh-don't use this one. My game crashed after I tried.
Chat with our AI personalities
No, there are no holidays except for weekends.
"Aging off" or (on)
You could always download things off the sims 2 website
No, you cannot have Sims 2 pets on Sims 3. You must have Sims 3 pets for Sims 3 or Sims 2 pets for Sims 2.
No not as far as i know.