“How could it be a meikel fast for those who need it to be. It is either meikel for everyone or not.”
The halacha says that everyone should fast, and for those who just feel the ordinary hunger, fatigue, and discomfort of a fast that is the case. However, you do not have to be elderly or terminally ill or have some kind of disorder to qualify for the heter. There is a middle case of people who do not fast well and experience extreme symptoms who are not, however, endangering their lives by fasting and can therefore be exempt.
It should go without saying, but I’ll say it anyway– consult your LOR.