<human>: Hello everyone!

I have a 3.5 month old GSD, and she's a little ball of energy (which I expected).  

I started off just taking her on small walks, but it never seemed enough for her.

Sunday, I took her on a 3km (2miles?) walk and she was still full of spit and vinegar afterwards, doing laps around my front yard and generally being a crazy puppy.  So I increased to 4km (2.5miles?) on Monday, with a very similar result.

Today, I increased again to 5km (3 miles?), and afterwards she ran around the front yard a bit, and then wanted to go in and chew on her Kong and be calm, which seems good to me.

Now, I've looked around online a bit, and I see people saying things like, "only short walks"  for large breed dogs for the first year, as you shouldn't over exercise them.  I just don't know what that means, but I don't think 5km is short.

Could you distill the essence of the text into 1-3 sentences?
<bot>: Is a 5km walk too long for a 3.5 month old GSD, even if she seems happy with it?