[Protoman]

In register.php

find:

PHP Code:

if ($year < ($current['year'] - 13) OR ($year == ($current['year'] - 13) AND $month <= $current['month'])) 


Above it put:

PHP Code:

if ($year < $current['year']-110)
    {
            eval(print_standard_error('error_too_old'));
    } 


add a new phrase in AdminCP..

Type: Front-End Error Message
VarName: too_old
Text: Sorry, but you must be living to join the site.

change the 110 above to however many years back you want it to limit membership.