Presuming from the terms that u have used such as " delayed falling of milk teeth " and " awkward eruption " I can understated u have done enough study by urself or u have consulted a doc .
Considering your child has been diagnosed with what u have stated then u can very well opt for braces treatment . That can help to correct ur concern of " awkward eruption "
Coming to ur worry of age :- there are 2 ways
1- myofunctional appliance- given at the age of 7-8yrs .
These help in regulating the direction of growth of the bone that helps in aligning the teeth
2- braces which can be given from 10-11 yrs of age
These help in regulating the direction of eruption of teeth or align the already erupted teeth .
Next Steps
Plz consult ur dentist to make the right treatment plan , and also plz notice if ur child has any other deformity or growth problems as there are possibilities he might be having some other systemic issues which are sometimes clubbed with dental manifestations Also .
To rule out this factor u will have to consult ur general physician too .