Is Arda earth?

[Hookbill the Goomba]

We are supposed to live in Seventh Age right now.

Correct me if I am well of course, but I heard that, in one of the HoME books Christopher Tolkien referees to the birth of Christ and "It hailed a new age of the earth" was I lied to? Or does this mean that we are now in "The first age of Christ" or something like that?

[Sharkû]

Christian references in the History of Middle-earth are very vague at best, such as in the Atrabeth. There's no instance of anything as concrete as what you mentioned, unless I'm gravely misremembering or blatantly ignoring something obvious.

[Legolas]

was I lied to? Or does this mean that we are now in "The first age of Christ" or something like that?

Maybe you were confusing that with reality...the "age" we're in has been referred to as AD, Latin 'anno Domini' - "in the year of our Lord."

[Hookbill the Goomba]

the "age" we're in has been referred to as AD, Latin 'anno Domini' - "in the year of our Lord."

When i said "the first age of Christ or something like that" I was merely making a suggestion of what the ages may be called if the information is true.

[Amarie of the Vanyar]

In this thread Seven Ages , there is an attempt of establish which event could be the end of each of the Seven Ages