I created my sim on the 25th but every time I check my age it turns it into the current date and says I'm 1 day old. Any help would be greatly appreciated. Thanks
It incrementally increases with each day. Create a sim at the beginning of the first day of the month and they will be '1' day old. The date doesn't matter for age, it's just how long since you have created the sim, basically.
EDIT: Okay I didn't read the issue properly, seems that the sims age is not increasing over 1 day. Thank you Raeven!