The only problem with putting a baby in such a big tank is their ability to catch their food. Of course, if he is having trouble you could always take him out and feed him in something seperate, like a plastic tubberware container, which is what I do with my beardies, even if they are big enough to catch them because I have found that crickets like to escape into ornaments in the cage.
But, in regards to a 55 gallon... I would prefer getting something wider with a width of at least 18". 55 are too narrow for an older beardy that gets to be about 17-24" in length. They need enough room to turn around properly.
My suggestion to you would to either stick with a 40 gallon breeder if a 75 is too big for you. I personally use a 75 gallon tank, used, that only cost me 50 bucks. Look around on craigslist.com. There are tons of used and/or new tanks on their from people who do not need them any longer.