Ensuring your affairs are in order in case of tragedy is something every adult should do regardless of age. Deciding guardianship of your children, inheritors of assets, and any other business items you may have. While it's all stressful, it can get even more stressful when asking people to be your child's guardian and come in with conditions.
I (F23) have been told I will be my sister's guardian if anything happens to my parents. She is 33 and has some disabilities. She is currently living in a group home. My parents have ensured that they have accessed every resource available for her to ensure she has as good a life as possible. The government pays for a good portion of the cost but not all.
We were visiting her this last weekend when they brought it up again. They are both reasonably healthy but had health scares in the previous few years. They once again said that I would be her guardian.