Great Northern peach cold resistant. don't how to upload pics
Neem oil is good for preventive control of some pests and diseases, but not necessarily for advanced conditions.
It's necessary to identify the pest or disease in order to advise on controls.
Pests that can put holes in leaves are grasshoppers, caterpillars (larva of moth), beetles and snails.
Are you sure they are bug holes and not shot hole fungus?
https://www.gardeningknowhow.com/plant-problems/disease/shot-hole-disease-fungus.htm
...and how do I fix it?
This is a fungal disease; Peach Leaf Curl.
This article will help you.
https://www.gardeningknowhow.com/edible/fruits/peach/peach-leaf-curl.htm
this is a dwarf peach tree in a very large planter
Without seeing it, this sounds like overwatering. It could be other issues, depending on what you have, or have not fed it, and amount of sunlight that it receives. In container, usually, it is overwatering that will kill a tree.
Make sure to only water once the soil is dry down to a depth of about 3 inches or so before watering again. This will prevent issues in the future. They also need full sun, so the more light you can give it the better. If this is indoors, you will need at least 200 watts of horticultural grade lighting per tree to get fruit.
Fertilization will also be necessary, frequently, in container.
This article will help you to grow these in container: https://www.gardeningknowhow.com/edible/fruits/peach/growing-peaches-in-containers.htm
After thining to 6" apart, I sprayed my peachtrees every 7-10 days for three months with captan and malathion. I had not infestation from plum curculio (like last year), but my peaches did not get very big, about the size of small lemons. They developed very slowly and then began to rot on the tree before ripening.
Captan is not registered for use on Peach Trees.
Malathion must not be sprayed on Peaches 7 days before harvest.
These articles may help you.
https://www.gardeningknowhow.com/edible/fruits/peach/common-peach-diseases.htm
https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-thinning.htm
https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-thinning.htm
https://www.gardeningknowhow.com/edible/fruits/fegen/reasons-for-small-hard-fruit.htm
One day they weren't there, the next they were.
There are, likely, a few things that you have around the house already that can help here. This collection of articles will give you information on how to craft your own pest control, along with many other tips: https://www.gardeningknowhow.com/special/organic
How long can you store a peach pit before planting - in a story I'm writing, I have one 8 years old, and wondered if it's too old? Also, does it have to have a cold first winter in order to germinate? Many thanks.
It is doubtful a peach seed would be viable after 8 years, but hey, is this a fiction book? And yes, the peach seed would need a cold period to germinate. Here is more:
https://www.gardeningknowhow.com/edible/fruits/peach/saving-peach-seeds.htm
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/storing-seeds.htm
Cam you tell me what might be the ailment here with this young Red Baron Peach tree
Your peach tree is under stress. Look for signs of disease (I did see some spots that could be fungal), insects, lack of nutrients and water. Call your cooperative extension agent if you can't find the reason for your tree to start changing colors. These articles should help:
https://www.gardeningknowhow.com/edible/fruits/peach/grow-red-baron-peach-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-leaves-turning-early.htm