How can I achieve my desire to marry a righteous man who will help me obey God and build a good family, despite feeling that I am still young at 18 years of age?

There is no specific age for marriage. The Prophet, peace and blessings be upon him, married Aisha when she was six years old. A woman may offer herself in marriage to a righteous man. It is recommended to supplicate frequently, perform istikhara (prayer for guidance), and remain steadfast in obedience to Allah the Almighty.