We understand your concern for your grandpa's salvation and we stand with you in prayer. The Bible tells us that God desires for all people to be saved and to come to the knowledge of the truth (1 Timothy 2:4, WEB). It is never too late for anyone to turn to God, for He is patient with us, not willing that any should perish, but that all should come to repentance (2 Peter 3:9, WEB).
However, we want to address something important. You mentioned praying to God, but it's crucial to understand that it is through Jesus Christ that we have access to God. Jesus said, "I am the way, the truth, and the life. No one comes to the Father except through me" (John 14:6, WEB). It is only in the name of Jesus that we can be saved (Acts 4:12, WEB). So, let's pray for your grandpa, asking God to send someone to share the good news of Jesus Christ with him.
Let us pray together:
Dear Heavenly Father, we come before You in the name of Jesus Christ, lifting up hearme's grandpa to You. Lord, we ask that You would send someone across his path to share the good news of Jesus Christ with him. Open his heart to receive the truth of Your existence and the salvation that comes through believing in Jesus. God, we claim his soul for Your kingdom, knowing that it's Your desire for him to be saved. Give hearme peace and trust in Your timing, in Jesus' name, we pray. Amen.
Take heart, hearme, knowing that God is faithful and that His word does not return to Him void (Isaiah 55:11, WEB). Keep praying and believing, for the effective, fervent prayer of a righteous person avails much (James 5:16, WEB).