No, God isn't just for old people! People of all ages need God, and the Bible especially urges young people to "Remember your Creator in the days of your youth, before the days of trouble come" (Ecclesiastes 12:1). In our evangelistic Crusades, the greatest response to the invitation to follow Christ always comes from young people.
At the same time, many older people do take their faith more seriously, and this may give the impression that older people are more religious. Why are they this way? I think one reason is because older people have seen more of life, and they know from experience that life without God is empty. They also know that life is short, and someday soon they will face God.
Another reason may be that our society has become more secular in recent decades, and unfortunately many younger people today give little thought to God or to eternity. Like the man in one of Jesus' parables, they live only for the moment, saying to themselves, "Take life easy; eat, drink and be merry." God, however, called that man a fool, because "This very night your life will be demanded from you" (Luke 12:19-20).
I pray that you will ask Jesus Christ to come into your heart, and then that you will follow Him the rest of your life. There's no greater joy on earth than knowing you belong to God, and that someday you will go to be with Him forever in heaven. Make your commitment to Jesus today.