Q:

Was the world life expectancy only 30 years at 1900?

In this article, About.com article on Life Expectancy they claim:

In 1900, the world life expectancy was approximately 30 years

I've also the same claim elsewhere.
However, this doesn't jibe with informal data-gathering I have done:

An arbitary search of Wikipedia of random people that I know lived and died (of natural causes) before the 20th century shows that almost all of them died over 30.
I was in an old cemetery the other day, and saw that very few of the people buried there pre-1900 was under 30 years.

So I understand my "research" is purely unscientific - e.g. to be on Wikipedia you have to be famous, which means you probably were wealthy, which means you probably increased your chances of living longer.
Still, I find it hard to imagine a world where 30 is the life expectancy - i.e. that roughly around half the people would die younger than 30.
I would like to hear further evidence supporting this fact or explanation for the fact.

A:

If you want to look on Wikipedia, here's a good place to start:
Table of Life Expectancy Variation Over Time
The table clearly shows that pretty much till mid-20th century, life expectancy was <30 years (aside from aristocracy).
As to why such a change in the last 100+ years, there are 3 main factors:

Child/infant mortality. From the same Wikipedia article:

The percentage of children born in London who died before the age of five decreased from 74.5% in 1730-1749 to 31.8% in 1810-1829. Ref 1;Ref 2

Even 30% infant mortality means that the "actual" life expectancy of, say, 50 years would turn into average TOTAL life expectancy of 30+ years. (Basic math - for population of 10 people, average life expectancy would be roughly (3*0.5+7*50)/100=351.5/10=35.15. This is VERY rough and not an actual statistical calculation accounting for distributions, but enough of an approximation to show the great effect on the #s)
Medicine. Most life-extending medical advances we take for granted are, at most, 120-150 years old (including antibiotics or, heck, sterilization). See this Timeline of Medicine and Medical Technology. A few among the late-19th/early 20th century are 1870-80s (Antiseptic practices, germ theory of disease, first vaccines by Pasteur); 1906 (Vitamins), 1928 (Penicillin). 
Widespread growth of the average wealth of society (e.g. economic surplus) allowed people who wouldn't have survived before 20th century (e.g. die of hunger/malnutrition/lack of vitamins/etc...) to survive. Before 19th century, a VERY large proportion of population live basically on the edge of subsistence.

A:

I don't think this data is available on a world scale. Remember, many countries didn't do any census stuff before the start of the previous century, and many still don't. Wolfram Alpha has some data available. This one, for instance, is the life expectancy at birth for The Netherlands:
 
See the impact of the two world wars? Interestingly, the Netherlands didn't even participate in WWI...
The US data Wolfram has, starts in the 1930s:  

UK:  
 
Iceland:  

You can try some more countries for yourself, but most countries don't have data before the '40s (at least not in Wolfram Alpha's database)  

