When does celiac disease generally develop?

Any age. Alrhough celiac disease can reveal itself when very young with a 'classic group' of symptoms, there are many older adults with celiac disase thar is diagnosed only after a thorough 'workup' of iron deficiency anemia - that may simply have presented as gradual fatigue - erroneously attributed to 'old age' by the patient - and sometimes others too :(.
Any age. A person can start showing signs of celiac disease at any age. However, it is common for a child at about 2 years of age to start showing symptoms since that is when wheat has been introduced into the diet.