My niece was six years old and talking to her grandfather. She loved Grandpa. She frowned as she had a thought. She said, "If you don't become a Christian, I won't be able to see you in heaven." It was true. Grandpa wasn't a Christian. These words from his precious little granddaughter pierced his heart as nothing else could.
He began to look for a church in Hong Kong. He found friends who were Christians and they took him to a church. Grandpa gave his life to Jesus and lived for him. My niece, now a grown woman, will see her grandpa in heaven. Isaiah 11:6 King James Version says, "a little child shall lead them." God uses the pure in heart of all ages.
Satan loves to make you feel useless. You're too old or too young to do anything significant for God. That's not true. God can use you no matter how old or how young you are.