I think that a 55 year old man has had many life experiences that a 20 year old girl would not understand. I think that your twenties are the time to live life to the fullest; this will be hard with a man that could be your father at your side. My advice: date someone you can grow old with.
Love is love. If you deep down inside, truly love a person, nobody can take that away, despite how old the companions are. In society's eyes, a 20 year old dating a 55 year old is very strange and weird.
Probably not. There is a huge gap of experience in a 35 year age difference, and the long term chances of this working out well are very small. Of course, if he has tons of money, and she's willing to wait......... ;-)