I tell myself my parents aren't getting older
Are you worried about your parents getting older?
Yeah, I just want them to be around forever.
That's really nice of you to say but you shouldn't take your time with them for granted by tricking yourself into thinking they'll be here forever. Cherish the time you have and make the most of it before it's too late or you'll end up regretting it.
I'm only a teenager, so I have time.
You never know what the future may hold. Anything can happen to you or your parents, so show them how much you love and care for them every day. Focus on the present and try not to worry about the inevitable.