My husband was officially diagnosed at 58. Our son was 18 and daughter was 20 but, as is usually the case, my husband had shown signs for several years prior to diagnosis, so much of their teenaged years has been impacted by their father's changing behaviour.
There is no right or wrong way to act and our son and daughter approached matters in completely different ways. My son automatically grasped the situation and was happy to take guidance from me on how to handle different scenarios as they unfolded. I wouldn't say that he found any of it easy, but he bit the bullet and did whatever was needed.
My daughter, on the other hand, spent the first four years after diagnosis working on the belief that her father was somehow in control of his actions and could do better if he tried - but that he didn't want to.
It wasn't until my husband first went into a secure unit following a crisis that it finally hit her that he really was ill - and from then on her attitude changed.
She could never bring herself to be a hands on carer, and fair enough, why should she? He wouldn't have wanted that and I was able to do that myself anyway. However, what she did do was help in other ways - ie sit for an hour with her dad while I caught up on sleep, pick up things from the shop if I'd forgotten something, collect medication if her dad was too restless for me to take him out, give her dad a hug and show him various medals she had won from a variety of marathons she was taking part in.
She was never at ease with her dad's illness and it definitely didn't get easier as the disease progressed, but by helping and supporting me, she was still helping and supporting the care and well-being of her father.
I suppose what I am trying to say is please don't feel guilty if you cannot bring yourself to do what you think is expected of you. See what you can do to help in ways that are more comfortable to you. As the disease progresses your mother will welcome support in whichever way you feel able to give it.
My husband passed away nearly three months ago now and I can honestly say I do not value the help offered by either one of our children as being better or worse than that offered by the other. They each played a huge part in caring for and helping me care for their father and it was because of them both that I was able to see things through to their conclusion.
By being part of it all in their different ways, both our son and daughter grew closer to their father, learnt patience and acceptance, put aside any past hurts or misconceptions - and I would say we all came out the other side of things much stronger than ever as a family.