I'm a sucker for lore and using the elements of the game's canon where I can, but the fact of the matter is, not many people take CoH's lore seriously when creating their own characters. At best, it's a grain of salt for them to base things around, and at worst, it's ignored completely for the sake of their own stories.
At a glance, even Phantom Marvel would be no exception to this experience. That said, it's become highly accepted to just let it go when it comes to lore and RP. Additionally, given that the Rikti Invasion that changed everything originally occurred in 2002 (https://paragonwiki.com/wiki/Rikti_Invasion_(Narrative)), and the general consensus for the current year (in order to avoid splintering the already confusing-at-times lore) is that it's 2019 where things have continued in a business-as-usual mode, that gives plenty of time for heroes that were around post Rikti invasion to have aged well. Additionally, it's quite literally been so long that teenage characters born in Paragon City wouldn't even know what a world without War Walls was like (kind of a scary thought!)
Anyway, that's all just food for thought and some of my opinions sprinkled in.
To stay on topic: my favorite minor aspect to RP out, personally, is the recognition of Security Levels and their purpose. A friend of mine even wrote in his bio a somewhat flowery, but extremely well written, short story about his hero identification card.
