sons

I have been wondering about mothers relationships with adult sons and when or whether mothers should let them go.
I have observed many friends who don't let their sons go - I have a relative who regularly goes to concerts with her son and his girlfriend - always has, he is 23 now...I find it creepy is it just me?
Am I just trying to justify my son's behaviour which leaves me somewhat out of things because he is very busy with job and wife and children and wanting to put a positive spin for all the other grans and mums who feel somewhat sidelined?
Is it just life? That they have to separate to become founders of their own families. Am I just jealous of these mothers who still have doting adult sons? probably, a bit. We are mothers after all and we have invested so much time energy and love and hope over the years.
I have another friend who I think encouraged the break up of her sons marriage from day 1...now he is divorcing wife and spends much of his time with his mother who is co-parenting his daughter with her mother.
I have seen another son change from being an irresposible drop out thorn in his somewhat smothering mothers side who after her very sad death morphed into man who married and now has two children and is very successful and happy. His dreadlocks were off by the time of her funeral. How sad for his mum my best friend who always thought him useless yet over indulged him. How tragic that she never saw him as a grown up.
What do you think, what have you observed? Am I on the right track or should I demand more from my son?