I've never actually heard of people only going by real-life age -- to use a drastic example, I would happily PB Michael Caine as a 32-year-old in icons from The Ipcress File, because that's how old he was at the time. Because the icons used are, well, what you're actually going to be seeing in-game. Natalie Portman was 12 or so during Leon: The Professional, so you shouldn't reject those icons for a young teen just because she's 34 now, imo?
If there's a large disparity between old role/current age, it just requires your player specifically naming the role/era/iconset they're going to use, and you making sure the PB was the right age then and that they're using the right icons. But yeah, that's pretty common practice to me. I've seen tons of younger-role PBs used with age-appropriate icons.