There is the other end of the spectrum, being Old. Becoming Old is to be avoided at all costs. Old People are rigid in their opinions, tied to their traditions, afraid of change, feeble in their movements, dull in their conversations.
There seem to be only two options, you are either Young or Old.
Many re-enactors are taught to measure the success of their "Look" against a photograph from the era. The closer they come to matching that photograph, the more successful their portrayal is deemed. There is a major pitfall in this method for the menfolk. The men who portray soldiers are looking at photographs of young men. The average enlisted soldier of the Civil War era was 22 years of age. The average age of officers was 26 years of age. Theaverage age of the men portraying those soldiers and officers is older, often much older. They still hold their Look up to photographs to compare.
So by the time the re-enactor portraying a soldier makes the decision to add a civilian portrayal, he's looked at hundreds of photographs of men in their late teens and twenties.
When searching out a photograph of a civilian to emulate, they gravitate towards photographs of the young men who look like soldiers out of uniform.
When they are presented with a photograph of a man in his late-middle years he looks stodgy, formal, Old... they are not that Old. They can't use that photo of an Old man because they are still young, active, vibrant men... just with responsibilities, family, civic activism, occupational experience... but they aren't "Old".
In the mid 19th century, Society took a different view of the middle years. They still encouraged the Young to enjoy a time of learning responsibility with a safety net and they still eshewed becoming Old as a burden to be avoided as long as possible. There was also a time in the middle.
Men in their middle years had the best of both Young and Old. They had the energy, optimism, and vibrancy of youth tempered with the authority, experience, and sense to enact change. Men in their middle years are the foundation of mid 19th century family and society. They are the civic leaders who bring their communities through War. They are the business leaders who bring trade, commerce, industry, technology, and social justice into the modern world.
In short, that stodgy man with dark hair, impressive beard, and a frock coat is not Old. He's an active, vibrant man affecting change on his world... just like you, Dear Newbie.
So, how does this paragon of Middle Age dress?
He chooses his attire based on the tasks of the day, just like you do. What "Look" does he need his attire to convey?
If the answer is authority, responsibility, and stability; he will choose "business dress." For most of the 19th century, "business dress" meant a frock coat.
The fashions of frock coats changed up over the 19th century. A man in his late 40s in the 1860s would have lived through the introduction of a frock coat as the standard daywear, courted women in the frock coat at it's tightest, gone to War in a loosening frock, and luxuriated in the further loosening post-war styles... all before Ft. Sumter was fired upon. A frock coat was no more uncomfortable to him than a suitcoat is to a modern man. Perhaps not his favorite, but worn when appropriate because it IS the appropriate thing to wear in the situation.
In photo collections of university classes, the Professor is usually the one in the frock coat. While the scholars may show up in a square paletot of the latest fashionable cut, the professor would get a meeting with the Dean about "professional image" if he tried it.
The physician wears a frock coat because he needs his patients to have trust in his knowledge, learning, and techniques. He, too, needs to convey a seriousness, stability, and trustworthiness that comes from "professional" dress.
The lawyer, too, presents his cases in court and meets with clients in professional dress. The respectability, trustworthiness, and professionalism is conveyed through "professional" dress.
Were we to see these same men or any man of similar occupation at home on Sunday afternoon, or enjoying the Ag Fair or a base ball game, or having a drink with friends in the tavern; he may very well choose a loose paletot. Should he take leave of his practice to volunteer with the US Sanitary Commission or take the family on an educational Tour of Europe, again the loose paletot is the practical choice and any tailor worth his price would see he chooses conservatively fashionable style elements.
So too are blue jeans worn by men of all ages, but not necessarily the same style. The young men in "skinny" cuts differ from the men in middle years in "relaxed" or "classic" cuts, and differ too from working men in "boot cut" and "Western" cut.
The paletot we learn from Mr. DeVere on page 82 of his Handbook of Practical Cutting on the Center Point System (1866 edition) is,
"...one of the most elegant styles of overcoat, and the one which is best calculated to suit all figures, all classes, and all ages. It may be cut of every degree of fullness:
* there is the close-fitting style, so well calculated to display the graceful figure of youth and early manhood;
*there is the medium style, which, while it displays the figure to the best advantage, combines that ease and comfort desired by those who have reached maturity,
*we have the square-cut style, so generally preferred by men who are given to athletic sports, from the great facility it gives for muscular action;
*and lastly there are the looser-fitting styles, so admirably adapted for men of middle age, who have arrived at a certain degree of corpulency."
There are some styles that were worn by men of almost all ages, but the context of when, under what conditions, helps sort out the "spot on like a photograph" from a near miss.
When looking at photographs to choose a style... make sure several men of your actual age are wearing that style and pay attention to the situations under which that style is used in the 19th century.