John Calvin Commentary Exodus 7:6

"And Moses and Aaron did so; as Jehovah commanded them, so did they." — Exodus 7:6 (ASV)

And Moses and Aaron did. It is not for the sake of boasting that Moses reports his own obedience; rather, after having frankly confessed his hesitation, he now relates that he and his brother had more courage for the performance of their duties. In this, he shows that he, like his brother, was God’s minister, and that he himself brought no industry, talent, counsel, or dexterity, but simply obeyed God.

Still, from their example we must learn that just as we may not undertake anything except what God prescribes, so we ought to pursue obediently and without objection whatever He commands.

What follows regarding their age is meant for amplification, since it was not a common occurrence, considering the natural frailty and weariness of old age, that two men in their eighties should have actively engaged in such a difficult task.

For I do not agree with the opinion of those who think that their dignity was enhanced by their age. I admit that age is venerable, but Moses had far different views: namely, that by excluding all human means, he might celebrate God’s glory, who performed such a mighty work through men who were failing and decrepit with age.

For although their vigor was not yet diminished, their old age could have made them timid and could also have caused the people anxiety when they saw their leaders to be not only of advanced age but even, by nature, not far from the grave.