People advertise leopard gecko's as a very good starter pet.
Leopard gecko's can have many problems, and can be very costly. I would suggest not getting one, as if it does get ill the chances are the vet bill will be quite high, and for a 15 year old that would be tough.
They aren't as high maintenance as dogs or cats, but if you don't get some things right with them it can go belly up so to speak.
Don't believe everything you see on Google. I just say a video of someone dumping their newly hatches leopard gecko's in a bath of deep water to see if they would swim. Not very good.
You have come to the right place for advice.
They can live a while, and it can be a commitment, but thats what I love about these animals, they aren't like hamsters or gerbil's and will live quite a while depending on the right care. If you do decide to get one, let us know and we will show you how to care for it properly, because most care sheets can get it wrong.
Also, are you wanting a pet that you can hold? Or are you not bothered?
Are you definatley wanting something exotic?
If you are not wanting a hands on pet, which is low maintenance, get a tarantula. I have one and she is lovely. Male Chilean rose's will live about 10 years, I have a female who will live significantly longer. But you feed them a locust or a pinky/cricket every 1-2 weeks, and they are brilliant to watch. Also Chilean rose hair are very placid tarantulas, and they are great to show off. Also if I have a large amount of money in my house and burglaries have been happening around my neighbourhood I just stick the money in the tarantula tank