In the historical timeline at what point is the modern man of today, different than say someone who thought he was a modern man in the fifties? Is there a specific time for modern man? What traits does a man have to posses in order to be considered modern? Just because we live in a modern age, not everyone on the planet can be considered modern so why do we think of ourselves this way?

Depends on what you define as modern
Styles, ways of thinking, culture,
What was then new and different is old and out dated now whether the new is better or not that is the way things are looked at. I guess partly because young people can not appreciate the old because they follow the crowd. Like nowadays people think rap is THE music and they can not appreciate the music that really gave music its roots.

I think we mostly consider ourselves modern now because we have instant communication, conveniences and things they did not have back then.

"Modern", like "rich", or "beautiful", is a relative and comparative term, not an absolute one.

I think it's down to the clothes you wear... labels price etc.
The car you arrive at the latest gig in... some sporty number, customized... big exhaust
Blasting out the latest by Jay-z... bragging about where you come from and where your going too.

AS you get older it's the job you hold ,the car you drive and the house your buying, the clubs you belong to... golf etc.
Do your children go to private schools, boarding schools, university etc.etc.
Where you take your holidays.

AS a senior citizen... do you own your property, have you a private pension,do you have a holiday home abroad, have you a gardener also a cleaner.

I think modern man at any stage throughout the different eras, have always been the same, it's just the style of clothes, car and property that have changed.

Taxonomically, we're homo sapiens sapiens now. I don't remember just when they decided to add the extra sapiens but I think the use it for humans from somewhere around 2000BC on. I could be wrong on the date.