Spoilers Mockingjay questions

I think Katniss is in her thirties when she has kids.
I think her dream represented a near death experience. Katniss was in a kind of limbo, between the living and the dead. The birds in the sky were the dead that she loved. She wanted to die with them. But the ocean she was stuck in was like the pain of life, keeping her from dying. When she said Prim was trying to keep her afloat, I think that was when Prim was in that same state of near death. When Prim let go; I think that was when she died.
Her fire was self created, and it had gotten out of control. It threatened to consume her.

That's what it seemed like to me.

I don't know when she had kids, but to me, i think when she told prim to let go or whatever, prim was trying to extinguish the fire or save her or something, and then she caught fire and died.

Katniss is 32 when she has her kids. But it doesn't say for sure, it says 5, 10 up to 15 years.