What age Dog should i get when i go adopt/rescue my dog?

Hers some basic info on me. Im 15 and i come from a family of 5 (me being middle, child, with my brother being 17, and my sister being 4), ive been researching on dogs and how to take care of dogs for about 2 months now, because im so excited about getting one. My preferred breed will be a labrador retriever,... show more Hers some basic info on me. Im 15 and i come from a family of 5 (me being middle, child, with my brother being 17, and my sister being 4), ive been researching on dogs and how to take care of dogs for about 2 months now, because im so excited about getting one. My preferred breed will be a labrador retriever, golden ret. german shepherd, australian shepherd, or flat-coated retriever, or any mixes involving these breeds.
I know im adopting a dog or rescuing one from a shelter, theirs just one problem.

At first i wanted a puppy, but now that i think about it, puppys are a lot of hard-work and require training, where-as if i adopt a dog that isnt a small puppy it will be trained, have its shots, be house-broken, and probably be more behaved. However..who doesnt want a puppy? theyre pretty small and they are cute, but it doesnt last forever.

So besides a puppy, what age can i get that is posibly more-behaved than a puppy but yet is still sort of young? what year(s) would that be?
Update: forgot t add this. Yes i do actually have the time to take care of a puppy especially on weekends, and i also will be the one who will mostly spending time with the dog. I also am energetic and up for about 1-3 walks a day.
Update 2: OH, and can some1 tell me wut a mutt is exacltly? i dont want to make a whole new question 4 it.
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