I am also surprised at some of the responses here. I am 50-ish, and have a DD and DS in their early to mid 20's, and no WAY would I cancel on them, if we arranged to meet, unless there was a very good reason. I love their company, and I (and DH) are always there when they need us.
Someone said 'I'm 50 with adult children and I'm very tired of active parenting and advice seeking.' What a bizarre comment. Do you think someone should stop being a mother as soon as the child hit 18? 
Why the hell do some people have this mindset that as soon a child hits 18, they need to fuck off? They don't suddenly stop needing their mother when they hit 18. It's like the bizarre attitudes (from some) that's it's practically criminal behaviour for a young adult to be still living at home past the age of 21. And if they go to uni (at 18,) they must NEVER return. Indeed, make sure you get a one-bed bungalow so they never can!
Awful attitude towards your own children. And I say that as someone whose 2 have flown the nest, both left at 18 for uni, then moved in with their mates afterwards, then moved in with their partner - 15-30 miles from me and their dad (my DH.)
They are independent with successful careers, and are have no plans to live with us anytime soon, but if their life goes belly up for a bit, and they need to come home, they will be more than welcome. There will ALWAYS be a place for them here, and we will ALWAYS be here for them. And they know it.
I can't imagine why some people have such a horrible attitude, and say 'I have done my nurturing, and now I'm entitled to my me-time, and my kids can fuck off at 18, and stand on their own two feet.'
'My priority is ME now' How selfish and mean. And as for the 'mothers in their 50's' comment! PLEASE stop.
Not all mothers in their 50's are like this. Many are lovely, and some mothers in their 20's, 30's, 40,'s, and 60's, (and even older,) are awful!
The OP sounds insecure and fragile and in NEED of her mother's love. Is that not ALLOWED because she is a 'grown up' now? 
Jesus........... words fail me! 
@User74000007 Look after yourself. Sadly you probably won't ever be able to change your self-centred, selfish mother, but you can change how you react to her. You perhaps need to distance yourself from her, keep her at arms length, and try to not show you care. Eventually she will need you, and she needs to be careful, because if she treats you like shit too often, she may find she is a very lonely old woman in a few years time....