Of American-English origin, the phrase to send a boy to do a man’s work, and its variants, mean to ask someone young, ill-equipped or inexperienced to do difficult or complicated work.

This phrase usually occurs in negative contexts, especially as never send a boy to do a man’s work.

These are, in chronological order, the earliest occurrences of the phrase to send a boy to do a man’s work and variants that I have found:

1-: From the Newport Mercury (Newport, Rhode Island) of Saturday 4^th October 1856:

Advertising.—The marked success which has followed the vast scheme of advertising first carried out in the literary world by Mr. Bonner, of the New York Ledger, has induced others to imitate his example. The Ledger’s circulation is now estimated at 170,000 copies. Mr. Bonner has paid in some instances as high as $1200 for a single advertisement. Some people thought he was insane, and would certainly go down, but the circulation of his paper has steadily increased. This extraordinary instance of marked success should lead others to follow his plan of liberal advertising, with the certainty of an increased business.
The advice given above has been repeated again and again, and it is only occasionally that a man like Mr. Bonner, who understands the thing, will venture anything in the way of advertising for the sake of great gains. What would the venders of nostrums do without the columns of a newspaper to set forth the qualities of their wares? And one has only to look at the extent of their outlay in this way to be convinced that it must pay to advertise liberally. Of course the narrow-minded skin-flint will say that it is to the printer’s interest to cry up advertising; and so it is, for if his subscribers do not prosper, he cannot expect to live; and therefore he is continually pointing them to the right way, though there be few that find it. And why? They send a boy to do a man’s work. They do not venture into deep water, for fear there are no straws for them to catch at, and so they paddle about just where it is a little damp, and then wonder why they too do not feel the strength of the current in Fortune’s gold-stream. Advertising is just as sure to bring its own reward, as manuring a field will tell on the growing crops. Men now-a-days do not go poking along looking at signs when they want to buy articles: to the newspaper they turn as to a directory, and the information there obtained suffices to lead to the spot where they are sure of getting what is wanted. And every man of good character and engaged in any ordinary business, and who does not succeed as well as he might reasonably expect, will find that the loose screw is a neglect of advertising. And let him not think that merely notifying his friends and the public occasionally where he is to be found, will suffice. He should keep his name and business ever before them, sparing neither time, pains nor expense to make it known, and the returns will amply repay him in every particular.

2-: From one of the unconnected paragraphs making up the column Patent Hash, by ‘Mr. Carboy’, published in The New York Atlas (New York City, New York) of Sunday 30^th October 1859:

. . . . . Substituting poetry for prose, is like substituting the jingling of sleigh bells in a tower for the deep sonorous tone of the church bell, a hurdy gurdy in lieu of a cathedral organ,—a fish horn for a trombone. It is sending, as poets now are, a boy to do a man’s work.

3-: From an account of the defeat of the Union troops commanded by Major General Benjamin Butler (1818-1893), at Big Bethel, Virginia, on Monday 10^th June 1861, during the American Civil War (1861-65)—account published in The World (New York City, New York) of Wednesday 12^th June 1861:

General Butler seems determined to occupy the attention of the country; but on this occasion his own conduct, or that of his subordinates, or both, places him in a less favorable position than that which he has hitherto occupied. […]
[…]
[…] The great mistake, as far as we are now able to judge, appears to have been in the lack of prudent reconnoissance and preparation. The event showed that Gen. Butler sent a boy to do a man’s work. To pit field howitzers against rifled cannon, and to send out a body of raw troops, prepared only for a sharp hand-to-hand fight when they had formidable intrenchments to attack, is neither “magnificent” nor “war;” it is simply recklessness, more or less culpable according as it may be accompanied with circumstances more or less extenuating.

4-: From a special dispatch from Washington, D.C., published in The New-York Times (New York City, New York) of Wednesday 16^th October 1861:

THE POST OF DANGER AT LEWINSVILLE.

I was up to Lewinsville, this afternoon, or rather to the headquarters of Gen. Hancock, who occupies the post of danger and of honor, being on the extreme right of the main body on the other side of the Potomac. The rebel pickets were about two miles or two miles and a half from his post. Yesterday, they skirmished nearly all day, our folks at night being about fifteen head of cattle better off than they were in the morning, having captured them from the enemy. This morning the rebels put ten head more in the same field, evidently to decoy our boys in. They got more than a match, however, for our boys not only got the cattle, but drove back the rebels who were laying in ambush to catch them. Gen. Hancock campaigned it through Mexico, and was too old a soldier to be caught sending a boy to do a man’s work. The skirmish was hot, but our men were in greater force than the rebels calculated. We did not have a man wounded.