Why should I mind it? I'm not breastfeeding a 30-ish man, I'm breastfeeding a child.
If anyone said anything to me (they haven't - yet, except for a stupid GP who couldn't understand why I'd breastfed past 6 months, if at all!), I'd smile witheringly and ask them whether DS was in fact 30 and I'd not noticed.
DS is a child, David Walliams is a big man. Nobody would still be nursing a 30-year-old, so why the fuss?