I am still not having a great relationship with my sons, with very little communication and visits. I suppose I am going with the attitude that my son's are young adults and the parents are not the people they want to spend most of their time with.
I would say give your sons another 5 years or so.
Kids are not fully mature until around age 25. And although my kids are so much more successful than me, they have matured and want the advice and friendship with their father.
