system
Given the following post, respond as if you're commenting on Reddit:
human
[Futurama] What exactly was The Professor and Amy Wong's relationship? They acted intimately sometimes, and she was an intern for a very long time...
gpt
Amy was an intern for the Professor for 12 years while she completed her doctorate, but the Professor reveals that she was ready about 6 years before that. A year doctorate will often be three of four years, but it's not uncommon for it to take longer, especially when, as seen, it depends on experimental designs (a planetary ratchet) may take a long time to perfect. 

So why did it take an extra 6 years? From Amy's point of view, she has no reason to hurry. Her parents are rich and her life is just as she wants it. She can go out partying and having a good time and has no pressure from them to get a job and be married while she is in education. 

She grew up chubby and that left her with a huge drive for acceptance and the Professor is highly dependent on her in many ways and so being needed and wanted makes her feel safe. So for Amy there is no driver for her to push to be complete. It's only when she gets serious with Kif and her life is moving on, that she starts to show signs of wanting to be done with her internship and complete her doctorate. 

For the Professor, well, we know he has no problem using people for his own benefit and so it's no surprise he wanted to keep Amy around. He's stated in the past he likes having her near as she has the same blood type as him and so she's a potential blood/organ donor. A mixture of him forgetting to tell her that she can move on and wanting to have her around for personal/professional reasons, means that he was happy to keep her as long as possible. 

Also, as life expectancy is much longer, you can easily life to 160, at which point you are supposed to go to the near Death Star, but it seems that many do not. So with double the life, people are more relaxed about taking their time in life.