One get those who surrender their lives at a young age to God, like Timothy. Others are called when they are adults, like the Apostles, others when they are old, like Abraham.
In Mat.20:1-16 Jesus tells the parable of workers hired on different times of the day. At the end of the day all received the same pay, which made the early birds grumble, but the Master was firmly in control of His own generosity. With this parable Jesus make it clear that it's never too late to surrender your life to the Gospel. In fact, latecomers are most welcome.