The phrase "days of existence" is correct and usable in written English.
You can use it any time to refer to the length of time something has been in existence. For example, "The United Nations has seen seventy-five days of existence since its founding."
In only fifteen days of existence, the Pizzagate subreddit had attracted twenty thousand subscribers.
In just 17 days of existence, the "secret" Facebook group has become the sudden online home of passionate Clinton enthusiasts.
A TWO-PARTY coalithat that briefly held control of the Suffolk County Legislature appears to have collapsed after only days of existence.
The topics of that unproduced screenplay by this brand-name producer include his last days of existence, his vision of a made-by-Disney metropolis and his thoughts on life after Walt, as it affects the rest of the world.
His unilateral suspension of devolved government on February 12th, after a mere 72 days of existence, saved Mr Trimble, who had promised his party that he would resign by then if the IRA had made no move on decommissioning.
While Hipster's initial launch page had over 10,000 signups in its first few days of existence, the startup's actual user numbers for SXSW were at just over 4,000 for the entire three day period.
Members of the freshly minted House Tea Party Caucus spent their first day of existence Wednesday trying to clarify just who they are — a tricky task when the Tea Party opposes big government and the caucus members work in the heart of it.
On Dose's first day of existence, its most successful list was called "23 Photos of People from All Over the World Next to How Much Food They Eat Per Day".
Membership was, and is, by invitation only, and in the first days of its existence a horde of aspiring new friends and trusted acquaintances clamored to get in.
For the 22 days of its existence, the balloon offered the possibility, in its randomness, of getting lost, of losing oneself, in contradistinction to the grid of precise, rectangular pathways under our feet.
What appeals to me is that it is a predecessor of the Natural History Museum in Kensington, and in the early days of its existence was the venue for the most famous debate about Darwinism, between Thomas Huxley – who became known as "Darwin's Bulldog" for the vehemence of his argument – and the Bishop of Oxford.
