I think the intensity of it must ease but I guess you are always going to 'worry' about your kids whatever stage of life they are at, you may be giving advice and helping them out all the way through. I know my parents do - my life would be really quite different without them.
My Mum still frets about us - well, mostly my brother if I'm honest (he is a liability though). He's 32 and I'm 35. Afaic, you never stop being a parent - but at some point you have to take a back seat and let your children live their own lives/make their own mistakes.