You don't show us how using a global hash fails for you, but here is an approach:

use strict;
use vars qw(%IsMember);

%IsMember = ('age' => 1, 'old' => 1, 'years' => 1);
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Use it as:

if ($IsMember{age}) { print "'age' is a member\n" };
if ($IsMember{ego}) { print "'ego' is a member\n" };
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For development, you can lock the hash keys by using Tie::Hash::FixedKeys.