To calculate chronological age in Excel, you can use the DATEDIF function. Here's how:

1. In a new cell, enter the formula "=DATEDIF(A2,TODAY(),"y")", where A2 is the cell containing the date of birth and "y" stands for years. This will calculate the number of years between the date of birth and today's date.
   
2. In another cell, enter the formula "=DATEDIF(A2,TODAY(),"ym")", where A2 is the cell containing the date of birth and "ym" stands for months. This will calculate the number of months between the date of birth and today's date.
   
3. To combine the two results, you can use the "&" symbol to join them together. For example, if the first formula is in cell B2 and the second formula is in cell C2, you can enter the formula "=B2&" years, "&C2&" months"" in a new cell. This will display the result as "9 years, 0 months" for the example you provided.
   

Note that the DATEDIF function is a bit tricky to use, as it doesn't appear in the function list and requires you to enter the arguments manually. The syntax is "=DATEDIF(start_date,end_date,unit)", where start_date and end_date are the two dates you want to calculate the difference between, and unit is the unit of time you want to use (e.g. "y" for years, "m" for months, "d" for days).