Is it possible for a betta to grow larger after it's a year old?

After a year in a 5 gal I moved him to a 20 gal. He's getting more food and exercise (chasing other fish a little) and I swear he's changing. He's just a regular red one but he seems bigger now and has several reflective blue scales speckling his body now. Is he maturing or is this from the new living conditions?