Age calculation between DOB and StartDate broken down into years, months, and days if possible

I need to create a custom calculation between two dates in my form. I have a Date of Birth (DOB) field and a Start Date (SD) field. I need to be able to input these two dates in a form and have a separate field called Age at Start (Age) to calculate the age broken down into Years, Months, and Days (ie. 4yrs, 2m, 26d). I've searched everywhere and haven't found anything that would breakdown the age. Any help would be greatly appreciated. Thank you in advance.