Unlike JO, there is no minimum age to compete in T&T. You can also enter T&T at any level.
This coach was talking about having this child ready for T&T nationals. Nationals begin at level 5, so he wanted to start at least at level 5. Level 5 has two required double mini passes, and I think one of them does have a tuck off the DM. (It has been a few years since my ds competed level 5, so I could be wrong here.). Level 5 also has both front and back tucks on trampoline.
The youngest age group for level 5 is 8 and under, FYI. So he could compete next year or the next or the next and still be in the youngest group. There is no rush.
I think the coach isn't used to such young kids. He saw a kid some talent and potential and pushed too hard and too fast, training him the same way he would train a 10 or 15 year old. It just doesn't work that way.