He is going to seed

While reading a book I came upon a sentence where the auther described a person he met: he is big and hirsute, thirty-something, and going to seed.
I couuldn\'t figure out what the seed means. Ask my huaband and he told me this: going to seed here means this man is getting old. When a plant is old and mature, it\'s giong to have seeds. I think the auther is using the metaphor.