seeds Can old seeds make it?

What is the oldest seed you successfully germinated and grew to a mature healthy plant? What is the oldest that didn't make it?
 
I am curious. I had >4 year Loco pepper seeds stored inside dried out peppers we normaly used for cooking. I tried to grow it into a plant, didn't make it. So this is how it went. At the germination stage seeds were constantly moist, properly heated and in soil. My other seeds germinated in 5 days. This old seeds however germinated only because I was patient and wanted to know if they can make it. They did, it took them more than 3 weeks to poke out! But they did.
 
Thing is none of them grew cotyledons.. They just grew a bit, constantly kept their seed helmet on and just couldn't push out those cotyledons. My other pepper plants had 3-6 true leaves at this point mind you, when the last Loco seedling that survived finnaly dried out (due to too much sun) and died.
 
Now I wonder, would such old seed make it if I properly cared for it? I shouldn't expose him to so much sun. Should I just cary on patiently waiting, or was such an old seed doomed anyway? I think old seeds lack proper stored energy or something but perhaps if it makes out of the shell things look good? I just don't know...

some seeds have been thought to go dormant for thousands of years and still be viable. Hard to say with pepper plants though..
 

The oldest mature seed that has grown into a viable plant was a Judean date palm seed about 2,000 years old, recovered from excavations at Herod the Great's palace on Masada in Israel. It was germinated in 2005.[4][5][6][7] (For more details refer to Judean date palm: Germination of 2000-year-old seed).
 

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I've never had need/desire to germinate seeds that were more than a few years old. I do put a piece of paper with the date the seeds were gathered in a ziploc. That said, things to keep in mind are the same as for any other seed:
 
- The seed must have come from a pod that was ripe enough for the seeds to be viable in the first place;
- The seed should be given a bath in a mix of hydrogen peroxide and water to eradicate any unseen pathogens before germinating;
- The seed must have been kept dry and at a cool enough temperature to prevent it from cooking. 
 
Yes, same goes for care after germination as for any other seed sprouted - if the seed casing won't come off on its own, gently remove it. If started indoors harden off. Keep moist but not wet.
 
Note that your sprout did grow cotyledons, they were what was stuck inside the seed casing. The cotyledons not only feed the developing plant, but also breathe for it until true leaves take over. No air, no plant.

It will vary by the seed type and the conditions under which they have been kept.  There really isn't a way to make a definitive determination without actually attempting to germinate them.
 
I've had 3 year old pepper seeds successfully germinate without issue.
 
For your specific situation, it sounds like the seed case (helmet) was very dried out and thus less pliant than a newer seed.  The cotyledons could not push off the seed case.  A longer pre-soak might have softened it up enough that they could have succeeded, or you could have stepped in with some mechanical assistance (a steady hand, some tweezers and nail clippers) to assist.

If a helmet won't come off on its own, you can spray it down with water to soften it then pinch it along the seem to make the opening wider for easier removal. Some are still stubborn after that, and when that happens wait another day then try again.

I  just sprouted seeds that were Pre 2006 (some as old as 2002 or 3).
Some sprouted almost 100%,some took a month+ to sprout,some didn't do squat.
Grew some colorful molds..
 
It didn't seem to matter if they were Chinense or?
Some of the Annuums did well while others didn't,same with Chinense etc.
 
All the old seeds I tried were kept under the same conditions...
 
I have only found that most of the time,Wilds HAVE to be fresh to grow well,in general.
 
Everything, I think is up to that specific seeds genes,ability to survive.

Simple answer: If it sprouts, it should make it like any other pepper plant. Most of the time, the trouble is getting them to germinate. Apparently they were stored well enough to keep the tiny drop of moisture in the seed from drying out. The fact that they had helmet head has more to do with planting depth than seed age. Try planting some more a tiny bit deeper and see what happens. Good luck!

I just don't know what happened though. It seems it dried out, my other saplings got burned also but they were big with true leaves so some of them got slightly burned at the tips, some of them nothing.
 
Was it the fact that we had more than one week of bad cloudy weather and then all of a sudden hot sunny weather, was it the fact they were moved outside with no window in front of them, or was it the fact that they badly needed water. Is it possible that plants are more prone to sunburn if they lack sufficient water?