You can add that as a column in the Client Screen. Settings > Options > Display > From Client information select Taxpayer age and/or Spouse Age and put in the display, then move up or down to where you want them to show.
No promises made or implied, I am just another user, like you.
I have asked in prior year to add this function as a box or window in screen 1 & 2 next to the dates of birth that tells you the person's age as of December 31 of the tax year. It is important facts when entering this information and I need to spend a few seconds to calculate their age to continue a discussion.