You could also use IO::Prompter, which I only recently learned about.

#!/usr/bin/perl

use strict;
use warnings;
use feature qw/say/;

use IO::Prompter;

my %responses = ();
my @prompts = (
    ["startamount",     "the starting amount",          ""],
    ["startage",        "your current age",             ""],
    ["endage",          "the age you want to retire",   sub { $_ >= $r
+esponses{'startage'} } ],
    ["yearlydeposit",   "amount deposited per year",    ""],
    ["annualinterest",  "the Annual interest rate",     ""],
    ["expectedmoney",   "Expected Retirement Money",    ""],
);

foreach my $prompt (@prompts) {
    $responses{$prompt->[0]} = prompt "Enter $prompt->[1]:", -num => $
+prompt->[2]
}

foreach (sort keys %responses) {
    say "$_: $responses{$_}";
}
[download]

There's probably a better way of specifying empty constraints -- though the OP will likely some constraints that goes beyond "it's a number" imposed on most of the input.