Bacall's character is only supposed to be in her mid-20s, but she always looked a bit older to me than her actual age. In 1953, the year HTMAM came out, she turned 29 (still 28 when filming), but if I didn't know that I'd peg her at about 32 or 33 -- not hugely older, but a few years, and that was true in most of her movies. Even in her first film, To Have and Have Not (1944), which she filmed while still only 19, she seems more like 24 or so.
I don't think she looked older than Grable (37 in 1953), but she definitely looks older than Monroe (27), as in fact she was. The biggest age difference between actress and character was Betty Grable, who was clearly supposed to be in her mid-to-late 20s, like the other two.