[Rachael x]

I have heard that Frontline spot on is the best flea treatment.
I was wondering do I treat my pup for fleas before she gets them in order to prevent it or do I have to wait until she actually gets them?
How old should you start treating your dog for fleas?
She is 11 weeks old now and dosnt have fleas but she has started to go out for walks and I was wondering if I could prevent an infestation in any way?
And do they have to be a recommended weight before treated with Frontline?

Thanks