The Guard of Counsels became the Imperial Guard in 1804, the year that Napoleon became the Emperor. Napoleon set the requirements for entry into it as 10 years of service, participating in several campaigns and a clean record and he "personally passed on every buck private admitted into its ranks". It is my impression that Napoleon was very hesitant about committing the infantry elements of the Old Guard on the battlefield whereas the cavalry and artillery elements were more frequently engaged, (source, Swords Around The Throne, John R. Elting, 1988, page 103 to 205).
Just an opinion, but I don't think that any Civil War armies were "professional" enough, or long serving enough to form elite brigades of what might be called shock troops.
I have believed for some time but have no source for this, that McClellan intended that the regular U.S infantry regiments and artillery batteries of the Army of The Potomac be considered as his Old Guard, but that also is just an opinion. I am not at all sure that he used them that way.
John