The second point is suitability.
We all have dreams, ideals, flights of fancy. Young people, especially, want to fly. And that is a very good thing - we'd never have saints if people never aspired beyond mediocrity.
When it comes to the call of God, we have to be a bit practical. God does not call a fish to be a bird. If a certain life is impossible for me, I am not called to live it. Period.
That is an amazingly freeing thought. If I can't do it, he does not expect me to.
Now, that does not mean that he won't ask demanding, difficult, top-of the bar. Not in the least. But it does mean that if I have something in me or in my life that makes a certain form of life impossible for me, then I should not even give it a second thought.
So what are the pre-requisites for religious life? Good physical, mental and moral health. Appropriate maturity. Those are the basics. If I do not have good physical health, a demanding physical regimen is not going to work (and religious life requires it). If I have serious mental health concerns, the challenge of silence, the work of prayer and the stresses of common life are going to be beyond me. If my moral life has been a shambles and I am just stepping on to the path of virtue, the demands of "the way of perfection" will be more that I am up for.
Does that mean I am not called to be a saint? In no way. It may very well mean, however, that this particular path is not God's call for me.
But, what if I am strong, healthy and a moral athlete (if only in the minor leagues)? Well, then, you might just want to consider...