Most Christians if they are asked "why do they believe in the existence of God " the general conclusion in the study point to the fact that perhaps they were born from Christian homes and were raised from childhood going to church, therefore they find themselves believing or they were convinced either by experience or situation to become Christians.

Nothing is wrong with that!
Only that your truth that God do exist is subjective, therefore there is no way you can make an objective argument to support your view since all the while you have been depending on your pastors/parents and didn't have a critical independent study of the scripture to show yourself approved.

2 Timothy 2:15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.

But what is an objective believing?
It comes from so much knowledge of the truth such that, at every point in time you are able to defend your faith because you are very sure.

Acts 17:16 Now while Paul waited for them at Athens, his spirit was stirred in him, when he saw the city wholly given to idolatry.
Acts 17:17 Therefore disputed he in the synagogue with the Jews, and with the devout persons, and in the market daily with them that met with him.

This was how sure Paul was pertaining to his faith. He was so sure that he went into the synagogue of Judaism and market places of idol worshippers to argue with them and win souls for Christ all because he studied first.
It was like going into a mosque of Muslims to consistently argue with them that Jesus Christ is the way.

An objective truth does not depend on the opinion of the one saying it, it stand on it own separately. Therefore it is not subjected to human emotions, church doctrines or creed
An objective truth does not even depend on God. It stand on it own separately from God even though it may be pre-determined by God.

John 1:14 And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.

John 14:6 Jesus saith unto him I am the way, the truth, and the life: no man cometh unto the Father, but by me .

So, the objective truth can never be subjective, there is a limit to which we can know as humans but beyond our five senses, there is the spirit, that spirit stand or exist on it own independently.

good

Nice day