Actually, the original published scripts suggests that Mrs. Paroo was around 14 when she gave birth to Marian. (I've mentioned this here several times.) Mrs. Paroo is described as being around 40 in the stage directions. No age is given for Marian, but Harold guesses that she is around 26.
How about Victor Garber for Trotter, Nathan Lane for Christopher Wren, Len Cariou for Giles, Anita Gillette for Molly, Penny Fuller for Miss Caswell, Frank Langella for Paravicini, Bambi Linn for Mrs. Boyle, and John Cullum for Major Metcalf. :)