Your comments made me curious, so I went looking on the web to see what I could find. The oldest tally sticks (the Ishango Bone, the Lebombo Bone, and the Wolf Bone) known are from about 20,000 to 35,000 years ago. From looking at images of them, it's hard to piece out specific patterns. There definitely does not appear to be a tendency to group tally marks into groups, the way we often do now. For whoever made this, if they wanted 21 tally marks, they just made 21 lines, not 4 groups of 5 plus 1 more, or a group of 12 and a group of 9. There definitely doesn't seem to be a tendency with any of these things to group marks into dozens or anything like it.

But the Ishango Bone in particular has some very interesting groupings, including some that add up to 60. It sounds like nobody is exactly sure what these were used for, or knows what the significance of the numbers was.

Conserve energy. Commute with the Hamiltonian.