Determining the ages, Tolkien's great use of Mathematics and Historic Events.

[Voralphion]

Shortly after Noah's Flood it is writen that in the days of Peleg, the Earth was Divided (Gondwanaland was broken into contients). Could this be something similar to what happened at the end of the 2nd Age?

I don't think the flooding of Beleriand could be Noah's flood. Middle Eath wasn't drastically changed after that, (Beleriand was destroyed but that was it). More change happened in the drowning of Numenor, when the world was made round and new lands created.

In regards to Son of Numenor's reply regarding the supposed age of the sphinx, I too have thought of that, (there are also apparently other things that are believed to be of about 10000BC as well), but I don't think those ideas were around when Tolkien was alive so he can't have used them in his estimation of the time between the fourth age and our time.