The question of when and if to get a pet is an important one for adults. It really depends on where you live and where you're at in your life. One of my best friend's mom is currently sending her listings for fish tanks that are 50% off. Her mom's a marine biologist, so it makes sense as a suggestion. Unfortunately, my friend has killed every plant she's laid her hands on recently, so I don't think she's ready to enter the complex world of raising a fish.
One of my other friends is much more responsible than me. She got a cat immediately after graduating college, and she's so good at taking care of him. I can barely take care of myself, let alone a fish, a cat, or, god forbid, a dog. Domesticated animals require so much attention and love, and I'm happy just getting two weeks of love from my parent's dogs every year.