Marriage Is Also For Companionship
Ge 2:18 And the LORD God said, "It is not good that man should be alone; I will make him a helper comparable to him."
People who think inappropriately of an elderly man who marries again later in life are people who only reveal the dirt they have in their minds. Marriage is also for companionship.
(Tip: Find a lifetime partner that you can be good friends with. A husband or a wife who is not a good friend will be a bad companion)
Keeping a pet is only a superficial solution. After God said in verse 18 that "it is not good that man to be alone" He then proceeded to show Adam his need for a companion that is comparable to his nature.
He let Adam examine all the animals in the Garden to make him aware of his need. Adam's giving of names to the animals required close examination into the nature of the animals. Thus proving to himself that he really needed someone who had the same nature as his. They came by pairs, with partners of like natures, but he had none:
Ge 2:19 Out of the ground the LORD God formed every beast of the field and every bird of the air, and brought them to Adam to see what he would call them. And whatever Adam called each living creature, that was its name.
20 So Adam gave names to all cattle, to the birds of the air, and to every beast of the field. BUT FOR ADAM THERE WAS NOT FOUND A HELPER COMPARABLE TO HIM.
If irresponsible children won't carve out time to give a widowed elderly parent meaningful companionship, marrying again is a legitimate solution.
Convinced of his need, God then proceeded to give him a companion comparable to him:
Ge 2:21 And the LORD God caused a deep sleep to fall on Adam, and he slept; and He took one of his ribs, and closed up the flesh in its place.
22 Then the rib which the LORD God had taken from man He made into a woman, and He brought her to the man.