Albert Barnes on Acts 4:22

For the man, etc. The age of the man is mentioned to show the certainty and greatness of the miracle. If it had been a man who had been lame but a few years, or if it had been a child or a very young man, the case would not have been so remarkable. But, after a continuance of forty years, all hope of healing him by any ordinary means must have been abandoned; and all pretence that this was jugglery or deception must have been absurd.