Yes, I understand completely.
My mother died at age 45, when I was 10 years old.
It is probably the reason why I married young and had children young (age 19 when I married and 21 when my first child was born) because I always worried about dying young.
I would like compare the feeling of grief like wearing a coat that I can't take off. It's always on me and some days or even years, the coat is light and on other days it is heavy and I just can't move with it on.
Well, then let's add the clock that is ticking and you're the only one that hears it. It's the age of your mother's last year. My mother lived 45 years and 208 days. When I turned 45, I was hyper-sensitive to everything. I had realized how young she really was and I just felt terribly sad on and off.
The day of my 45th year and 208th day, was very solemn. And then, I experienced my 45th year and 209th day of life. Life. I was so grateful and that doom I had felt on and off throughout my life was gone. I was so much lighter. Remember that coat? I don't notice it much anymore. I'm 52 now and I still have it on me but I've learned to acknowledge it and feel grateful that I was so loved by her and I loved her so much back. I changed my perspective of it. Obviously, it took 35 years.
I'm sorry OP for your loss.