my %hash = (
	a => ['15-19',30,35,120],
	b => ['15-17','30-35',40],
	c => ['15-18',30,35,120],
);

for (values %hash) {
	@$_ = map {/^(\d+)-(\d+)$/ ? ($1..$2) : $_} @$_;
}

use Data::Dumper;
print Dumper(\%hash);