I don't know what 13th age is. We can all guess what D&D5 is.
Anything prefaced with "PirateCat's" is probably going to be good.
You owe it to your grandchildren who will be amazed by your tales of how you played in the very first sessions of TimeWatch.
to do otherwise would be like saying, "Sorry, I don't have time for that" to the funny man standing next to the blue police box when he asks if you'd like to see the Zanzibarbarians of Deneb Prime.
If your group will play D&D, but not 5E, perhaps they'd play Ghosts of Dragonspear Castle with an earlier ruleset. If it is meant to be run with 5E but 5E is meant to run like earlier editions, it might be interesting to see how it runs with an earlier ruleset of the group's choosing.
I've posted to this effect before but I still see WFRP as WKRP, as in WKRP in Cincinnati, and I thought that would be a slightly odd campaign - trying to make a second-rate radio station profitable and dealing with quirky personalities like Les Nessman and Dr. Johnny Fever.