I just don't see the point of having your life and joy come to a screeching halt indefinitely because someone died. The fact is that EVERYONE is going to die sometime. It's part of being a human.
So, describe this. Is someone in your life having this problem? Are you sure that that is the problem? Have you talked gently with them about it? Do you want to help? Is it your business?
I haven't met anyone like you've described, though my MIL is close. But her problem is that she wasted 40+ years of her life with an abusive man, and had her whole identity wrapped up in looking the other way, in accepting expensive jewelry every time she found out about a new other woman, in believing the lie she HAD TO KNOW was being told about money and everything related to money...that now that he's gone, left her with NO life insurance and 50K worth of debt to the IRS, no life insurance b/c he forged her signature to borrow almost all the value in it (we found his files of practice signatures), now I think she's throwing herself into what a fabulous man he was, in order to avoid the realization that he wasn't worth all of that, and to move on would mean she has to realize that. She won't even sell the stupid jewelry to pay the debt all at once....sigh.
But other than her, I don't know anyone just like you describe.
You were an older child when your mom died. Those that I've known who lost their parents as children do seem to take it differently. It might be that the brain is still so malleable that you just take it in and go on, and it's MUCH different than what it would be like if the parent died later. I have a friend who lost both his parents inside 10 years of each other...mom as a teen, dad in his 20s, and he talked about his parents VERY differently than I did, as I dealt with the sudden death of my mom when I was 30 and she was 55.
So that might be a difference. If you lost your other parent now, you might have a very different reaction.
I have quite obviously moved on with my life, though I still grieve. I advanced in a job, I met my now husband, I had a kidlet, my relationships with relatives has drastically changed, etc etc etc. But...just last night I was watching TV and burst into tears at the Sally Field Boniva commercial, b/c she reminds me of my mom (didn't look a thing like her other than their size, but they were similar ages and Smokey and the Bandit was a HUGE fave at my house, LOL) and I wish my mom were alive. It's been almost 10 years (which causes a pain just to think about), but that still happens.
So just be careful about who you are judging to not have moved on...it might not be reality; you might just be seeing it through your filters...if you don't want the easily sad people to see your way of grieving through their filters negatively, don't do it to others.
I'm sorry your lost your mom so young.