...they were the last two remaining people on Earth?
I say no, it would not. Being fruitful and multiplying as soon as possible would be a "good" thing, based on my personal belief system. How about you?
This is a very hypothetical situation. The two people may have been separated from the people they loved and have wounds to the heart one may not see. The young woman may not be fecund and with ptsd on her doorstep, her lateness may be extended as long as it takes her to get over her losses. The 40-year-old man may have been driven to a vascetomy upon his second child's birth due to the high cost of raising children before virtually all other people died in some cataclysmic event or even an unknown plague which for some reason, the man and the girl were immune or not affected by the virus or other organism that caused the end of the rest of the people on earth.
The two would be drawn together by necessity, however, and if they planned a future together, she would have to be willing to have many children, and he would have to take care of a pregnant woman as well as one who was recuperating from childbirth plus the children she produced. My great-grandmother who was born in the generation following the civil war, bore her 23rd child in the year 1900. This child of 14 might not know the need for sanitation or even how to boil water to sanitize cotton fabrics or linen. Lately, the large stores featuring inexpensive clothes are producing rayon blends that have a half-life of about 3 months, and if you boiled some of them, they might melt. So I'm not sure a good prognosis would be in for a girl that young, with no help, could survive one pregnancy, much less 10 or 20. It would take a miracle of God to have a second Adam and Eve who were raised in this generation due to fabric technologies, few people farm, and fewer people raise animals. The odds of them being able to run a garden and farm after a year of starvation would be hit-and-miss factors of survival also.
It would definitely take faith to make it. Most people in this time have been brainwashed by teachers to make more demands on others than they accept. And schools are so busy promoting experimentalist agendas, basics of living and surviving are usually relegated to the boy and girl scouts, 4H in the country are probably the best teachers of surviving on a piece of land, although the Boy Scouts may offer workshops on surviving in the woods for a few days with only a knife, some cord, a tent, and a few cans of beans.
And with no other people around to help these two, I hope the local library was left intact so they could have information to help them out of their day-to-day dilemmas until they figured it all out.
Adam and Eve had a garden of Eden that provided year-round fruits and vegetables, and all that was necessary for people to live and walk about unclothed with no severe weather to make clothing a necessity.