How long does an iPad last?

My iPad is getting more and more unreliable. I have had the screen going black with the white apple logo almost every day lately. I know this means it is resetting itself, but every day? It is also a lot slower than it used to be. I have just checked when I bought it and it was March 2012. So only four years, maybe that is the norm these days. I use it every day for emails, the web and I have quite a lot of photos on it. But it looks as if it is dying. They are not cheap, are they. How long have you had your iPad? Has anyone had to replace theirs? I would be interested to know.