OP, I do empathise! There's a lot to process with this 'getting older' lark ...
For me the big issues have been / are:
Fading looks - don't think I am vain, but can't hide from the wrinkles and greys and 'spots' appearing on my hands - yuk!!! I do feel society places a lot of importance on looks and that other people start to bracket you.
grandparenthood - we all know it can rejuvenate us and that we have a great deal to give, but I have found that with some younger people, as soon as they hear the term, they can begin to relegate us at times and think we belong to another era.
work Currently between jobs and looking for a change, but not confident it will be easy to have someone take me on - even though I have another good 10-12 years left in me, have a pretty good CV and know I would be a fabulous find! 
I am a pretty confident person usually, but all these areas can trip me up and get me thinking negatively in ways I know I have to address and combat for myself. I think this is key - not letting yourself get into a downward spiral. Easier said than done, but someone wise said to me make a list of ten good things about yourself and when you are low return to it and re-read it. It is a good corrective over time.