Should I agree to marry a young man who is 10 years older than me and smokes, knowing that I performed Istikhara and nothing appeared to me?

When a Muslim woman considers marriage, she should look at the man's religiosity and character, for these are the foundation of a family's happiness in this world and the hereafter. A righteous man treats his wife with kindness, honors her, safeguards her rights, helps her obey Allah, and wishes good for her. A difference in age does not matter as long as it is not significant. If the man smokes, while still observing the obligations of Islam and avoiding major sins, and you believe you can help him reform, then there is no harm in marrying him; otherwise, it is not advisable.