In Japan there are possible ruins claimed by some to go back to 8000 BCE, though they are disputed as to whether they are man made or not.
Also in Japan is evidence of the world's oldest known structure, though post holes don't really make much of a building. They are from about 500,000 years ago.
In Malta there is the Neolithic temple of Hagar Qim, dated to around 3000 / 3500 BCE, and the Hypogeum there dated around 2500BCE.
Stonehenge dates to around 3500-5000 BCE.
Newgrange was built around 3200 BC, during the Neolithic period
The oldest pyramid is the Djoser Step Pyramid at Saqqara, Egypt, was constructed by Imhotep 2630 BCE.