That's an interesting question. On the one hand, children should be raised by a mother and father; on the other, being raised by a single Catholic father is far, far preferable to being "raised" by an agency. On the whole I don't see why it wouldn't be morally alright.

Practically speaking I think it's moot, I don't think the adoption agencies would accept it, though I could be wrong.

does not feel called to the married state but want the joys of parenthood by himself for himself and for care in old age..

Very troubling.......

It would not be an ideal situation for a child to be raised by a single man, any more than by a single woman. It would very much depend on the man and the circuмstances. I know of a single missionary woman doctor who adopted two children, siblings one of whom was disabled.

But the way OP has expressed it  

does not feel called to the married state but want the joys of parenthood by himself for himself and for care in old age..

I would say definitely not.

Nobody has a right to parenthood especially for the stated reasons.

There are great saints who made their life work the care of abandoned children, for the Love of God, not for selfish reasons.

Thanks for the reminder Soulguard.
Here's a little something:

from a letter written by Saint John of God  

If we look forward to receiving God's mercy, we can never fail to do good so long as we have the strength. For if we share with the poor, out of love for God, whatever he has given to us, we shall receive according to his promise a hundredfold in eternal happiness. What a fine profit, what a blessed reward! With outstretched arms he begs us to turn toward him, to weep for our sins, and to become the servants of love, first for ourselves, then for our neighbors. Just as water extinguishes a fire, so love wipes away sin.

So many poor people come here that I very often wonder how we can care for them all, but Jesus Christ provides all things and nourishes everyone. Many of them come to the house of God, because the city of Granada is large and very cold, especially now in winter. More than a hundred and ten are now living here, sick and healthy, servants and pilgrims. Since this house is open to everyone, it receives the sick of every type and condition: the crippled, the disabled, lepers, mutes, the insane, paralytics, those suffering from scurvy and those bearing the afflictions of old age, many children, and above all countless pilgrims and travelers, who come here, and for whom we furnish the fire, water, and salt, as well as the utensils to cook their food. And for all of this no payment is requested, yet Christ provides.

I work here on borrowed money, a prisoner for the sake of Jesus Christ. And often my debts are so pressing that I dare not go out of the house for fear of being seized by my creditors. Whenever I see so many poor brothers and neighbors of mine suffering beyond their strength and overwhelmed with so many physical or mental ills which I cannot alleviate, then I become exceedingly sorrowful; but I trust in Christ, who knows my heart. And so I say, "Woe to the man who trusts in men rather than in Christ."

You can be a spiritual father without adopting.

I think the question itself is problematic in the same way it is problematic when it is asked if gαys should be allowed to adopt.

Here is what I mean, it is presented from the perception of "rights" or what the adult wants.

It is not presented from the standpoint of what is in the best interests of the child.

I think it depends on the situation.  For example, I think it would be fine, perhaps even preferable, if an unmarried male relative (uncle, cousin, older brother, etc.) wanted to adopt a recently orphaned child.  In this situation, the child remains with his family, and would likely not be devoid of female authority figures, even if the adoptive father is single.

On the other hand, if a single man (or woman, for that matter) simply went to an adoption agency or orphanage looking to adopt a child, it would be far from ideal, and likely shouldn't be permitted, especially if there are married couples also seeking to adopt.