Can I store ammunition in my attic? I live in texas so cold wouldn't be that big of a factor. Heat might be

Heat would be a primary concern for the longevity of the powder.

Wrap them in paper and cardboard and tape the boxes shut so that you somewhat control the humidity and other environmental issues.....the cartridges will be fine for years

I suggest you put a thermometer in your attic before you put your ammo in there.

Or just go up there in the summer and set for a while.

I would NEVER put any ammo in an attic in Texas [or anywhere else for that matter].
Like wise I would not keep it, nor powder or primers in a garage.

Ammo is best kept in a cool dry place.

Put it in a closet, high enough off the floor so if a water pipe breaks it will not get wet.

I would not want to wrap it in paper or cardboard as that can attract moisture.

Best thing is to put it in Military ammo cans.
That way the ammo is protected.
The 20MM cans will hold a lot of ammo or powder.

Storing powder samples at 150°F is the old Army Ordnance method of predicting end of life. It goes bad in weeks to months at that temperature, and they had some formula for predicting how long it'd last under "normal" storage conditions from that. It could easily reach 150°F under a summertime Texas roof, I think. (And certainly does in parked cars.)

Powder store rules: cool dry place away from flame, heat, flamable sustances, electric discharges, but never hot, humidity place.Better, ever use fresh ammo or just reloaded.