How old is too old from a relationship perspective?

My current interest is approximately seven years older then I’ am. I’m aware that this attraction might only be temporary and is hesitant to take any action towards him; for crushes come and go. I’m still a student working towards getting a degree.

Do you have a age preference when hunting for your “SO”/limit?
If your already engaged with someone, what are the age differences if any?

This question also applies to dating younger men and women. Your thoughts?