This is a different situation for me, so I thought I'd ask your opinion!
Right now, I have an almost 4-year-old redfoot, Shellie. I also have an almost three-month-old hatchling RF named Padme. Since I've had Padme for almost the entire three months of her life, I've starting showing her to Shellie (with the blessing of their reputable vet). Shellie tries to bite P. Not nip, BITE. Okay, I don't really want to deal with half of a tort, so I just let her sniff. This does not occur in the habitat, because I know torts can get territorial.
Thing is, Shellie DID share the habitat with our yellowfoot, who was two years younger than S. They had no problems. I'm sure it is just the age difference. How large should I let Padme get before they can actually hang out? Last week's weigh in: Shellie was 1600 grams and Padme was 80 grams. Yes, Shellie is large...but not fat. She just had a growth spurt a little while ago. 
Here's a picture of Padme:
She was a life saver and my little tort is doing much better now that she is in better hands and not being picked on all the time. Good luck with yours. You might want to wait until Padme is bigger so she can hold her own with the other one.