When did the procedure to memorize and celebrate Anniversaries started ?

Well I love to celebrate birthdays and marriage anniversaries. It does not necessarily have to be very pompous or grand but in a very small way. I invite some few friends and family and cook for them. To me it is actually remembering the beauty and sweet memory of that day and making the day special for my loved one. It is like a family get-together also where we can spend some fun-time with our family and friends. I love to celebrate birthdays especially of my little son.

First things first. Answer for the first part of your question is, the practice of celebrating an occasion dates back to ages. We celebrate not only Anniversaries and Birthdays, we celebrate Festivals. Because they are not like the other days of our life. For example Deepavali is celebrated because it’s a special occasion. This day marks ‘the triumph of good over evil.’ Another special occasion is ‘Janmashtimi’ , the Birthday of Sri Krishna. In a nut shell we celebrate an occasion that signifies a specialty. Similarly. We celebrate ‘Sri Rama Navami because it marks a special occasion , Marriage day or anniversary of Rama and Sita.’ So it says that the practice of celebrating Birthdays and anniversaries is not an offshoot of Modernity.
But with the advent of colonial rule, these celebrations took a new turn. They are not just restricted to very special people. Fathers day, Mothers day, friendship day are a few examples wherein even a common man can be a subject for a celebration who have an important place in one’s life.
This practice has further taken deep roots in to society because, these celebrations have converted in to a ‘Big Business’ proposition, in the form of ‘Greeting cards’ business.

This must have started when marriages as an institution would have been incorporated in the society. people need some reference to celebrate the togetherness,

No one really know when this started. It probably started small by wishing each other and having a nice home cooked meal. But now with the increasing influence of corporate companies this is becoming more of a show. You have to throw big parties and give expensive gifts.

When Husband & wives started spending less time with each other!

It can be safely stated that the birthday and annivarsy celebrations followed the introduction of calendar.

I think this was to remind your partner that you have been tolerating them for so and so long period. As far as memorizing is concerned the successful people always tell their partners later "I forgot" saves money and energy. :)

Now a days most of them leading mechanical life to get out from that all are start celebrating this the special days in their life like birthdays,anniversary etc.

When did it start means no idea

Not sure of when these celebrations started but they certainly make for good memories.