Combine buttons, and have them switch direction with a second click.

This is a pretty standard feature across sorting UI. The buttons could be labeled as such:

[Modified] [Age] [Score]

As you click each one, an arrow appears to indicate if it's sorting ascending or descending:

[Modified ↑] [Age] [Score]

If you click it again, it switches direction:

[Modified ↓] [Age] [Score]

This will add additional functionality and reduce clutter.

Combine the oldest/newest buttons to "age", and have each button switch direction with a second click.

This is a pretty standard feature across sorting UI. The buttons could be labeled as such:

[Modified] [Age] [Score]

As you click each one, an arrow appears to indicate if it's sorting ascending or descending:

[Modified ↑] [Age] [Score]

If you click it again, it switches direction:

[Modified ↓] [Age] [Score]

This will add functionality and reduce clutter.