Reptile, Raiden, Kitana were dropped in MK3 along with many other characters and only added back in with Ultimate MK3. Even MK poster boy and Ed Boon favourite Scorpion didn't make the cut into MK3.
Back to the OP:
"Ageless"
Quan Chi
Raiden
Ermac
+25 years could be explained away without issue
Cyrax (robot)
Mileena (isn't she "born" in MK9? Not sure how Tarkatans age but the Edenian side lives for thousands of years. Regardless, if she was born in MK9 barring some horrible side-effects from her birth she would be like 26 at the end of MKX)
Sektor (robot)
+25 years will have an effect
Sonya Blade (forms basis of Cassie Cage, might crop up in story using move-set).
Johnny Cage (as above)
Kano (never portrayed as the youngest of people to begin with)
I have no idea how they age
Baraka
Reptile
Sheeva
Kinda. There has been a character named Sub Zero in each MK fighting game, but it hasn't always been the same person. MK1 is Bi Han who became Noob Saibot, MK2 is Kuai Liang (Bi Han's younger brother) who became Cyber Sub Zero in the "current" (MK9) timeline.