I cannot imagine an apple tree in your zone still being winter dormant. Look carefully below the graft to see if the stock shows any sign of life. Your graft may have failed or your rootstock may have died. You may scrape the bark and look for any green of the cambium layer. Al

I live in Orange County as well, all of my apple trees have had leaves and flowers for a while, your apple tree should at least be showing some signs of life now.

I'm in San Diego and my apple trees are full of apples. If yours hasn't leafed out yet, I would scratch the bark for any green. It may not be alive any longer.

Woo hoo, we have a leaf! It must be the world's slowest variety.

That is great to hear, it is always frustrating when a tree does not take so it is good to hear that is it coming along, albeit a bit slowly.

Sweet Sixteen is a high chill apple variety, and most likely will leaf out very, very late in Orange county because of the lack of Winter chill there. It will also grow very slowly as a by-product of the lack of required chill accumulation.