If it were me, I would worry. If she is 30 and single, she doesn't care how old he is.
My pioneer partner was 40 and "mentoring" a disturbed 20 year old in our congregation. His mother was one of our close friends, and he was very troubled. I was the only one who worried about how close they were getting and talked to her about it all the time, but she was obviously dazzled by this young man who was so obviously in love with her. Within months, they got married. She was taken off the pioneer rolls, and they were not allowed to use the KH, and had a problem finding someone to marry them, but finally did. The marriage lasted 7 years. Finally they divorced because they just had nothing in common. The age difference was too much. She had a 17 year old daughter at the time, but she was not a problem for them, but it emphasized the age difference.
So, yes.............be concerned!!