You get a weaker stream as you get older.

As men age, their prostates get larger and it can grow into the urethra tube and narrow it, potentially obstructing the urine stream and making it less forceful. A weaker pee stream isn't as much of an issue for older women, but it can still happen because the lining of the bladder and urethra become less flexible. If you're having a hard time peeing, apply heat to your lower abdomen to help relax muscles.