For an excellent rendition of the creation and construction of Stonehenge, you should read Edward Rutherford's book, "Sarum." It's historical fiction, but it contains the best possibility for construction I have read (and is an excellent book).
A relatively advanced civilization called the Beaker People are believed to have built Stonehenge
Stonehenge is a human structure. People did not find it, they built it. It is believed to have been the work of Neolithic tribes, in the period of two to three thousand BC.
It is believed that the Winter Solstice was celebrated by the Celts, the same group believed to build the Stonehenge. The Stonehenge appears to have been built to celebrate this time of year.
Stonehenge is thought to have been built by the beaker people.
People
The neolithic people of Britain built Stonehenge for unknown reasons. It has been found that the stones are aligned to tell where the sun will appear at the Winter Solstice. There are burials located nearby. Some theorize that it was a meeting place for trade. For many years, people believed incorrectly it was built by the druids, they constructed it supposedly for sacrificial ceremonies. Stonehenge is entirely prehistoric in construction.
Stonehenge was built by people so the answer to your question is no.
Stonehenge is not a natural formation, it was built by people.
Stonehenge was first seen by the ancient people who built it.
Not century but millennium. Stonehenge was built around 5000 years ago, but nobody knows for absolute certainty.
No it was not built by Egyptians
The major stones of Stonehenge are mostly sandstone, others are igneous rocks.