So im seeking help in understanding more how others work in past eras and dead ages from eons past into their realm. as an example im working on six ages, the age of titan, the primordial age, the age of humanoid kind the age of cursed, the classic dnd age, and the age of the future aka the new world

It might be a good idea to think of general bullet points for each age to begin with. Nothing too detailed but things that are common knowledge to have happened such as the creation/birth of the races or in which age certain well known current or former empires and kingdoms began and/or fell. Maybe any long lasting wars that helped shape the course of history (Like the Giant and Dragon wars from the Forgotten Realms). Maybe add some creation myths for the early ages and explain how the gods revealed themselves to the mortals if they weren't there to begin with. Possibly also roughly how each age began and ended.

Those rough bullet can then be a good guide for when you need to later flesh out certain parts of your lore for story purposes. It's ok to leave some parts blank, sometimes chucks of history is lost. It's also ok sometimes to change the lore up between races in small ways, different races will remember the past differently. 

Ages and Eras can mean different things.  One (world-ages) can be defined by truly world-shaping events that effect everyone in your world and are a common point of reference no matter where you are.  Another type of age can be more local, and less "earth shattering" and based on more mundane things.  

An example of the former in my world:  the most recent world age began with the creation and launching of 6 world anchors (mountain-sized constructs of magic, stone, and metal) into various locations in the Multiverse to stop an Elder Being (Great Old One) from ripping the continent from the Material Plane and pulling it into the Far Realm.  The age began with celebration at the stop of the cataclysm and then 100 years of war as kingdoms and political entities fought for control over the anchor points (which became powerful sources of magic in the new age), eventually coalescing into four large political entities that persist into the current time.  

An example of the latter would be the foundation of the island castle of Safe Haven in the Kingdom of Eastport (one of the four political entities), and the shift of that country from a fairly typical dispersed feudal government headed by a king to an oligarchy of isolated nobles removed from the day to day of the country, and the inevitable decline of the culture and civilization as criminal empires sprang up to fill the power gap and the ever growing decadence of the new ruling class drained the resources of the common people.  This "age" change doesn't affect any of the other 3 political entities, but is important for the one kingdom it did affect.  

Ultimately, its probably not important to have a full history of your world written out.  Figure out the most important things the PCs need to know and start there...the rest can be added as your campaign progresses.

My world has had four different time periods, each new one beginning with a world changing event. 

The first time period is the Age of Creation (AC). This age spans 4479 years, encompassing the time since the creation of the gods up until the start of the first Dragon War (a war between the dragons and the giants). No humanoids existed at the time, but notable events include the creation the Aboreon (basically good aligned Aboleth), the creation of the six Krakens, the creation of an actual continent (the world was an infinite ocean beforehand), the creation of the Tarrasque, and, of course, the creation of the giants and the dragons (who went to war two years later).

The second time period was the Dragon Age (DA). It included the entirety of the Dragon Wars, world spanning battles between the dragons and the giants. It took up a full 1721 years, most of which were filled with bloodshed. Notable occurrences include the creation of the first few mortal species (elves, dwarves, humans, and halflings), the birth of the first half-elf, and the Coalition of Three Races, and alliance between the elves, dwarves, and humans that would persist for over two thousand years. This age ended when a failed spell of catastrophic power leveled a mountain range, killing thousands of both dragons and giants (who only numbered in the thousands overall). 

The third time period was called the Heroic Era (HE), and it was, overall, the golden age of mortals. It had its ups and downs, but it got its name for a reason. This was when most of the history that my players will uncover is from. It spanned a full 2562 years, and included more world shaking events than I can list here. Some major ones were the creation of the dragonborn and orcs by the dragons and giants, respectively, the categorization of dragons by color, the corruption of the drow by Lolth, the discovery of a lot of new magic, and the birth of the first lich. This era ended when a portal opened to the Abyss, causing an immense demonic incursion.

The current time period is the Dark Era (DE). It was supposed to be called the Reunification Era (RE)... but the government propaganda didn't really work to cover up what happened. The demonic incursion had broken half the world, twisting it into a realm of darkness and pain. The elves and dwarves had fled, and the human kingdom of Galoron bore the brunt of the war. In the end, the gods sacrificed themselves to seal the demons in the Abyss. With Galoron in chaos, four powerful (immortal) archmagi instilled themselves as kings, ruling over the people as tyrants. Still, they managed to build Galoron back up (even if they did declare war on pretty much everyone). And even now, 106 years later, no one's really recovered from the horrors that the war enacted upon the world. 

My world has 4 ages. The first age had basically nothing. Any creatures from that age went extinct by the middle of the next age. The first 3 gods/goddesses appeared in this age.

The second age was basically the age you want to live in. There are now 200 gods/goddesses including the original 3. There is a lot of magic and there are not a lot of huge monsters until the end of this age. It's just the best age out of all of them in the world.

The third age is the beginning of the downfall of the world. There are only 12 gods/goddesses including the original 3. Things are really bad in the beginning of the age (Storms, plagues, earthquakes...) It gets better near the end of the age, though. All of my characters that are from this world are from the second half of this age.

The fourth and final age is when the world is destroyed. All of the gods/goddesses disappeared and everything except humanoids and monsters disappeared as well. (The world was very reliant on the gods/goddesses.) The humanoids didn't last long after this, and so the world is basically just a flat area of land filled with dragons, tarrasques, and other monsters. So yeah... a complete history of my homebrew world. (If you are wondering, the world lasted to be 60,000 years old...)

So, yeah. Those are my example ages from my homebrew world.