Romans 4:19 

Without becoming weak in faith he considered his own body, now as good as dead (for producing children) since he was about a hundred years old, and (he considered) the deadness of Sarah’s womb.

Having children at 100 years old would not be possible in the minds of all of us today. Abraham did not stagger at unbelief. God said He would provide, and Abraham knows God is able. The world around us is full of doubt and unbelief, and if we listen to the world over the Word, we will fail. Our focus matters, and what we spend time around matters.