In regard to pre-WWI service breeches, the cut & style of your breeches appear to be closest to the 1907 & 1909 pattern. However, they do appear to be tailor made rather than a pair of regulation or "issued" service breeches.
I say the 1907 & 1909 patterns, because earlier specification breeches all had the suspender buttons on the outside of the waistband, as opposed to the suspender buttons on the 1907 through 1909 service breeches, which were all sewn on the inside of the waistband, not the outside. Also, the amount of "flare" on the posted breeches seems to match the amount of flare on the 1907 - 1909 styles. Earlier and later patterns were made with less of a taper or flare on the sides.
With the exception of the 1901 Khaki Riding Breeches, all regulation U.S. Army breeches made between 1903 & 1909 (Specification No's 610, 611, 632, 697, 698, 846, 878 & 1050) had two rear pockets in addition to the two front and one watch pocket. The rear pockets are missing from the breeches you posted.
The two rear pockets were however, omitted from the 1910, 1911 & 1912 pattern of service breeches. The rear pockets were reinstated on the 1917 pattern service breeches.
In addition, as previously mentioned, according to the various specifications for U.S. Army service breeches the style of breeches on your breeches seem to be different from those adopted by the army:
Regulation buttons in use between 1901 and 1919 were: brass - white metal without any inscription - non-rustable white metal without any inscription - composite white metal - vegetable ivory (Spec. No's 878 & 1050) & "Army Standard" white metal buttons which were inscribed with the initials "U.S.A." or the initials "U.S.A." and the word "Army".
I cannot be absolutely certain about this fact, because anomalies do exist. However, I believe that none of the above "white metal" buttons used by the army had a shiny chrome finish like those used on your breeches.