As my colleague, PCG senior editor Robin Valentine, pointed out in his seminal treatise against horniness in Baldur's Gate 3, "An adventuring party is basically like the Olympic Village, and we all know what goes on there." Your BG3 crew has this youthful vitality to it, but "youth" can mean very different things for Faerûn's fantasy races. Some spoilers for Shadowheart's Act 3 story ahead.
I've been around the block with D&D, so I know all about half-elves' average lifespan of 180 years or so, but it was still a small shock to look into Shadowheart's background late in the game and realize she was over 40 years old—the Sharran cleric notes this fact herself when exploring the entropy goddess' enclave, and you can also put two and two together from logbook dates in the enclave's archives.
A YouTube video from Headline_Olympics and a popular BG3 subreddit thread by TheDesktopNinja are united in their cry of "Shadowheart is HOW old?" While the comments are full of know-it-alls pointing out the anti-aging effects of Elf heritage (and also good skincare routines), I think it is a genuinely surprising little character detail, special elf rules or no. Shadowheart always struck me as one of the more naive and immature members of the party, something she shares with frenemy (and likely youngest member of the crew) Lae'zel.
This also had me pondering the rest of the party's ages. Wyll and Karlach are pretty much confirmed by the game to be 24 and around 29 respectively. Halsin's a spry 300, but as he moves into middle age he should seriously consider tapering down his steroid stack for the sake of his heart health.
Astarion's an odd one because, as an elf, he could have been well into his hundreds before ever becoming a vampire spawn. Gale, meanwhile, has the distinct energy of a Silicon Valley CEO in his 30s or 40s that the press insists on calling a "boy" or "young man" for some reason.