My opinion is that the maximum difference is 10 to 15 years. If the difference is greater, then people are just from different generations. I love my dad (he is older than me by 20 years), we are very similar, but I understand that we are people from different generations and have different views on life.
I often write men who are 60, 70 years and older. In the beginning, I tried to communicate with them, but understand that we are different. Now I'm not continue this communication - I don't want to lie and give any hope.