Young Earth

What I have been able to observe about languages seems to support the view that mankind is old - thousands of years old - but perhaps not as old as many have been told - not many tens of thousands of years old or older.

I've observed that it doesn't take very long for the language spoken in an entire region to completely change.

A brand new language - Tok Pisin - developed and spread all over the islands of Papua New Guinea, and is well on the way towards extinguishing hundreds of pre-existing languages. Not only did this take only about a hundred years to happen, but in that time the new language itself has also had time to undergo changes. 

The new language - Tom Pisin - borrows a word from one of the fast-disappearing indigenous Papua New Guinean languages, which shared that vocabulary from a Filipino language, which in turn got it from Spanish - and now the use of the word has become standard across Papua New Guinea. How long did it take for this influence to take place? Not thousands of years, only hundreds - beginning with Spain's influence in the Philippines only some hundreds of years ago.

Things change quickly on a large scale. One of the biggest migrations in known human history occurred not thousands but only hundreds of years ago - the migration of Europeans to Australia. English became the main language replacing many hundreds of pre-existing Aboriginal languages. This huge impact took only a couple of hundred years to happen, not thousands of years. The same could be said of the Americas.

Many south-east Asian and Pacific island languages seem related. Yet as far as we know the historical trunk of these branch nations dates back not too many thousands of years at the most. It took a relatively short time for different branch languages to form.

Many European languages have a common basis in Latin. Again, this influence happened over only not too many thousands of years.

Major changes and adaptions happen so quickly that it's easy to perceive that at a couple of thousand years BC there may have been only around say seventy languages in the world plus or minus a few. 

It's perceivable. 

I think a lot of things take place more quickly than perhaps we've been told - not only in linguistics, but also in geography and astronomy, to name a few.