What does this simple rebus mean?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

Rebus Puzzle Definition: A rebus is an illusion device that uses pictures to represent words or parts of words.
What does This Rebus Puzzle Identify?

I’m tall when I’m young, and I’m short when I’m old. What am I?

There are forty elephants and they have forty-fore heads. How can this be possible?

A man is walking down a road with a basket of eggs. As he
is walking he meets someone who buys one-half of his eggs
plus one-half of an egg.
He walks a little further and meets another person who buys
one-half of his eggs plus one-half of an egg.
After proceeding further he meets another person who buys
one-half of his eggs plus one half an egg. At this point, he
has sold all of his eggs, and he never broke an egg.
How many eggs did the man have to start with?

A man is surviving on an island along with his friend. They have been starving for four days for food. Suddenly, they find a fisherman. The friend goes with the fisherman in order to catch the fish (if they can find any).

The fisherman returns after some time but he is alone and has some salmon that he had prepared. When asked, the fisherman tells him that his best friend fell off the boat and drowned in the water. Starving for so long, he eats the meal while crying for his friend.

After being rescued, he goes to a diner and orders salmon. When he eats his meal, he jumps and commits suicide. Why did he do it?

Today, I celebrated my 32nd birthday but I was born in 1972.
How is this possible?

Lifeless eyes on my smiling face and watch your child's sleeping place. In their dreams they hold me tight. What am I?

All of the flowers I have are orchids except two. All of the flowers I have are hibiscuses except two. All of the flowers I have are roses except two.

Can you tell me how many flowers I have?