I’ve never been able to germinate watermelon seed more than 22 years old. Viability is extremely low after 12 years. I am growing Wibb watermelon this year from seed I saved in 2006. I started about 100 seed in a tray and wound up with 6 viable plants. I’ve also grown Anne Arundel melon seed that were 11 years old. I am growing a Romanian Melon, a cucumber, a gourd, Gills Golden squash (Pepo), Voynichero Blue squash (Maxima), Wisconsin Cheese squash (Moschata), and Sweet Red (Moschata) squash.
I tried unsuccessfully to start several other squash varieties from extremely old seed a few months ago. Glenn Drowns is attempting to bring several old varieties back from near extinction. We will succeed with a few of them. I store curcurbit seed in my deep freeze which significantly increases the length of time they retain viability.