Is it okay to give a young dog Missing Link Plus with glucosamine?

I have a 9 year old shepherd mix with bad knees and my vet recommended putting him on a glucosamine supplement. I've read good things about the Missing Link dietary supplement so I got the Plus formula that includes glucosamine and was giving it to both our dogs. Our other dog is a one year boston terrier and I know bostons are prone to knee problems as well ( I think its called luxating patella). I didn't think it would be a problem to give it to both, but on the manufacturer's website it only mentions "mature" dogs in the description for Missing Link Plus. Just want to make sure this is okay, or if I should put the young one on the original Missing Link formula.