I would go in with no prejudices against any of the rats. Go with your instinct and see which rats you connect with. I have adopted many rats, young and old, and the best ones were the rats that I felt a connection to, not the youngest.
I have had strong connections to rats which I obtained at 1 or 2 years old. Some of my strongest bonds were to rats that were adults when I got them. While I may have only had them for a few months or a year, I never regretted getting them. My short time with them was well worth the heartache that came from losing them.
You can start fresh with the older rats. There really is no difference, which is why it is better to choose the rats that you connect with best.
The best thing I ever obtained from owning rats was the ability to look beyond age when selecting a pet. I used to think you had to get a baby, but owning rats helped me to see that age does not matter, it is personality.
Some of my older rats that I adopted and still miss today: Marcus, Dexter, Avery, Homer, Buckley, and Brisby