I have two RTs and he's still pretty young because his beak is pretty small I'd say around 3 or 4 but you never know lol. Wilbur's beak is way bigger than that and I've had him for about 8 years now
When mine came to me and I asked on here lyn asked me to measure underneath. Mo was 4.5 inches from what I can recall and she said he was about 5 years old. Not sure if this helps