Will the Mahdi come in atleast within this lifetime or 80 years

I will be in my late 90s in 80 yrs will the Mahdi show up before that , I don't even think I will survive till I am 90 yrs old.

people keep saying this the end times and the Mahdi and Dajjal will show up soon but why are they not?
Has the Mahdi been born yet?

And is it haram to not think the world will be ending soon ?