I am not sure... but the ones I have are all about 10 years old and going strong.
I think many peoples parakeets die early because they just feed them a bad diet of only seeds and honey treads. They don't get a balanced diet then.
Mine get basic millet budgie mix and lots of fresh vegetable every day. They also are outside so they get vitamin D from the sunlight. I add multi vitamin drops to the drinking water about once or twice a week.. and they have mineral blocks for calcium and natural branches of fruit trees to rip apart.
I don't cut up the vegetables.. I just wash them.. and throw them in. Heads of broccoli, pealed carrots, cabbage hearts and all their favourites. They like the hard vegetable because the like to chew them up.
They absolute favourite is steamed yellow sweet corn. They love an entire corn cob to chew up. Keeps them entertained... but they only get corn about twice a month.. as I found it made them get really fat if they eat too much.
Finally they really need to be about to fly and be active. In a small cage they don't get enough exorcise and will get fat and unhealthy.
Either allow them to fly around your room every day.. or better still get a huge cage of aviary for them. Mine live in a smallish aviary in the garden.