as a Sorcerer, can i cast a Fireball using quicken and my bonus action then ready my action on someone's else turn to cast fireball again? Its not considered casting 2 leveled spells on the same turn right?
The relevant text is (important parts are bolded):
You take the Ready action to wait for a particular circumstance before you act. To do so, you take this action on your turn, which lets you act by taking a Reaction before the start of your next turn.
...
When you Ready a spell, you cast it as normal (expending any resources used to cast it) but hold its energy, which you release with your Reaction when the trigger occurs. To be readied, a spell must have a casting time of an action, and holding on to the spell’s magic requires Concentration, which you can maintain up to the start of your next turn. If your Concentration is broken, the spell dissipates without taking effect.
Just to expand on what sabin76 said: if this were allowed, it would effectively permit Sorcerers with Quickened Spell to ignore the one-spell-slot-per-turn limit entirely, since they could always just set the trigger for the Ready action to be "when the next turn starts" or something similar. If that were the intent, it would be built into Quickened Spell or a Sorcerer class feature.
As mentioned, when you Ready a spell, it's cast on the same turn, so you can't also cast Fireball using your Bonus Action. This is the same as in the 2014 rules.
As a suggestion, without Quickened Spell, you can Ready a cantrip (or a level 1+ spell through traits/features/feats that let characters cast them without using a spell slot), and cast a Bonus Action spell (leveled or not). Or vice versa.
But with Quickened Spell, there's an additional limitation: if you quicken a spell (cantrip or not), you can no longer cast a level 1+ spell, even without using a spell slot.
Quickened Spell
When you cast a spell that has a casting time of an action, you can spend 2 Sorcery Points to change the casting time to a Bonus Action for this casting. You can’t modify a spell in this way if you’ve already cast a level 1+ spell on the current turn, nor can you cast a level 1+ spell on this turn after modifying a spell in this way.
Finally, just one more idea. With or without Quickened Spell, you can Ready an action to activate a Magic Item to cast a leveled spell (or at least those that require the Magic action or one action), since you're not actually casting the spell on your turn when doing so.
as a Sorcerer, can i cast a Fireball using quicken and my bonus action then ready my action on someone's else turn to cast fireball again?
Its not considered casting 2 leveled spells on the same turn right?
You cannot.
The relevant text is (important parts are bolded):
Just to expand on what sabin76 said: if this were allowed, it would effectively permit Sorcerers with Quickened Spell to ignore the one-spell-slot-per-turn limit entirely, since they could always just set the trigger for the Ready action to be "when the next turn starts" or something similar. If that were the intent, it would be built into Quickened Spell or a Sorcerer class feature.
pronouns: he/she/they
As mentioned, when you Ready a spell, it's cast on the same turn, so you can't also cast Fireball using your Bonus Action. This is the same as in the 2014 rules.
As a suggestion, without Quickened Spell, you can Ready a cantrip (or a level 1+ spell through traits/features/feats that let characters cast them without using a spell slot), and cast a Bonus Action spell (leveled or not). Or vice versa.
But with Quickened Spell, there's an additional limitation: if you quicken a spell (cantrip or not), you can no longer cast a level 1+ spell, even without using a spell slot.
Finally, just one more idea. With or without Quickened Spell, you can Ready an action to activate a Magic Item to cast a leveled spell (or at least those that require the Magic action or one action), since you're not actually casting the spell on your turn when doing so.
Keep in mind that this particular thing isn't allowed anyway since the trigger for a Readied action must be "perceivable".
But yeah, the key here is that a Readied spell is technically cast when it is readied, not when it is released, so the idea in the OP doesn't work.