Hello.
I am a 19 year old man who is strongly considering conversion to the Catholic Church.
Are my prayers valid? Am I constantly in a state of my mortal sins since I haven’t gone to confession ever?
Would I go to hell if I were to die today?
Mortal sins are remitted through either Confession or an act of perfect contrition in which a person is sorry only through love of God, not fear of hell (imperfect contrition). Imperfect contrition is enough for Confession though. A person who made an act of Perfect Contrition validly should still confess to a priest before Communion. Such contrition is a special grace.
For this reason none of us here would be able to say if you are in a state of grace or not.
If a person wants to become Catholic but dies before that time, not having access to Confession, I also believe God takes that into account because their disposition was good and He might give them the grace of perfect contrition.
I wouldn’t worry about this too much and just work on becoming Catholic, and if you’re really concerned you can ask Our Lady to obtain perfect contrition for you even before your first Confession.
But you’re not in the same state as a person who doesn’t want the faith or Confession, in any case. God is acting in your life and you seem to be cooperating with His grace because you are seeking the Church.
As for your prayers, God listens to prayers even of people in mortal sin to help them with conversion and salvation. Even though prayers acquire supernatural merit in a state of grace, God would answer any persons prayers for the truth and graces needed for salvation.
God bless you! Try not to worry so much over your state, you are cooperating with God and coming towards the Church, and I believe He is pleased with this. He doesn’t ask the impossible. Ask Him for the grace to become Catholic and receive the Sacraments, and you can ask Him for perfect contrition too.