Gameobject stages - how to store it codewise?

This is a very hypothetical question.

How would I go about creating different stages for a gameobject?
Let’s say I have an entity. This entitycan only be in 3 different stages.
Let’s say: Thriving, Content and Dying.

What would be the best way codewise to store this condition in and also be able to make the entity change its state depending on certain prerequisites?

I could just do a bunch of else statements, but wouldn’t it be messy?

There are many ways you could do this, the simplest would be to just make an enum with your three states and switch it when necessary. If you find the conditions for switching the state to come up often or are very complex then you might consider looking into implementing a basic state machine.