How do you know if it is your voice or God”s voice?
The short of it is that if it is persistent, then you approach your diocesan vocation office and start there.
It may be that God is calling you.
It may be that you are “attached” to some aspects of the priesthood, and that it is not God calling you, but rather simply your attraction to some aspects of a priestly life.
And if between you and the diocesan vocations office you both come to the conclusion that you enter seminary, you will have anywhere from 4 to eight years (and possibly, more, should you discern an order) before the Church will call you to ordination.
I thought since the eighth grade that I wanted to be a priest; the pastor put the kibosh on my entering minor (high school) seminary. He was wise.
I entered the seminary in college, and after two years, it was clear to me that I did not have that vocation.
It most definitely was
not wasted time. I learned much, I am still in touch occasionally with some I was in seminary with, some of whom were ordained, and some, like me, who were not. And for those of us who did not go through to ordination, I don’t think any have thought it was a waste of time - rather, it was not our calling.
Note that I said “the Church call you”? Ultimately it is the diecision of the bishop - it obviously requires your cooperation, but the bishop can say, “um, no” - which happens rarely, but does happen.