Old dog afraid of new puppy

Several things to consider...
1) Is Milo typically nervous or afraid of other dogs, especially larger dogs?
2) What steps did you take to introduce them? Just plop the younger puppy down and go "here's our new friend"? Controlled meeting on neutral ground with both dogs leashed?
3) Did you let the puppy keep pestering him after he tried to get away?
4) Toy breeds tend to break, not bounce, and allowing the younger puppy to paw and pounce on Milo can lead o him being injured, possibly seriously.
5) Raising two puppies is four times the work of raising one, so returning the GSD to her breeder might be the best option.

Milo is afraid of any dog, doesn't matter the size of the dog,I introduce them at the dog park and I tried to have both on leash when I try to make milo play with the puppy

Then no, he's probably not going to get used to the GSD without a lot of work with a really good trainer and/or behaviorist.

Don't force him to play with the puppy -- that's making it worse. Can you put baby gates up in the bigger house? It might help if Milo can see the new pup but knows the pup can't get to him. Treat him for calmly watching the puppy, and vice versa. They need to get used to each other's presence without any contact. After a little while, you should get a better indication of whether they'll be able to interact in the future. Never leave them alone together when you're not home, regardless -- even in play, a large dog can hurt or kill a smaller one.

Keep them separate. That is the solution.
You cannot force a terrified dog to be un-terrified.