I think it would be more accurate to say that’s when the Information Age started. The 21st Century is a numerical term with a real definition but I get what you mean.
Protoboard, I believe what you have in mind is The Long 90’s, described here as being the transition period between the fall of the Berlin Wall and 9/11. I tend to agree.
On the 19th century debate - some historians recognize The Long 19th Century, being from the French Revolution to the First World War. Essentially a period of political upheaval, the rise of modern nation states in Europe, the Industrial Revolution, the railroad, the telephone and everything else that formed the foundation of the 20th century.
In particular, IMHO, the Industrial Revolution still forms the basis of modern jobs. People can talk about the “knowledge economy” all they want but I have had a real struggle trying to think of any modern jobs or professions that don’t basically operate on an industrial assembly line model. Modern industrial-corporate capitalism is built on the concept of “take X product or service and churn through it as quickly as possible while still somehow managing to maintain frequently unrealistic expectations of quality in the exercise of maximizing profits.” Whether it’s putting together gizmos, flipping burgers, answering phone calls in a call center, processing paperwork (nowadays mostly on a computer screen) in a bank or other kind of office, bagging groceries, clipping people’s hair, even seeing patients as a doctor or dentist, we are all mostly glorified assembly line workers. The white collar ones just get to work in air conditioned factories and use computers as their machines of choice.