If you want the background sharp, you want to close down the lense and have the background near your subject. Check dof master here:
Online Depth of Field Calculator to lean more about deph of field.
Using a 85mm f/1.4 for a head shoot (say 2m shooting distance), you get 3cm of deph of field at f/1.4. if the eye is in focus, the nose is not. At f/16 you get 32cm in focus just enough to have everything in focus if the guy is on the wall that serve as background. A wall that would need some texture for the sharpness to show.
Even on 5m setting, you get only 18cm of deph of field at f/1.4. You'd need f/4 or f/5.6 to ensure you have a sharp near background and f/22 would still give only 3.2meters of deph of field.
The resolution figure you see are anyway the very fine details of the smaller skin hair that would appear only if you zoom at 100% on a computer or look with a magnifying glass on a 30x40" print.
For getting the character as you want, what you need is micro constrast and the performance of the lense bellow 1500 LW/PH with the best possible contrast at theses settings. Very high resoltion results are typically irelevant for what you are after are they are for all portraiture related work.
You don't need a big lense, you don't need wide apperture. You need a lense with punchy colors/constrast and also to master you post processing skills.
Look to the next shoots why one would get a wide apperture lense. Most of the subject is out of focus and the background is completly blured to make the subject pop. This help soften the rendering, hide the skin defects (even through you can see them on the boy by zooming)
FA77 f/1.8
FA77 f/2
Look then how much more visible and contrasty a picture look like (with the same FA77 f/1.8) closed down to f/4.5... How much more it make all the skin defects more visible. See how the background is still completely blured because it was taken outside:
FA77 f/4.5
To me a constrasty and much cheaper lense would do a better job. That can be a macro lense, a type of lense that excell at sharpness and high contrast (DFA50 macro, DFA100 macro, sigma 70 macro) and is often avoided for portraiture because it is too sharp, too constrasty and not enough forgiving. But that what you are for. This kind of lense is also sharp borders to border.
You can also rely on a DA70. Very constrasty and punchy colors. FA77 or FA43 would add more 3D/pop to the rendering. That can be interresting.
One thing is sure, you should not care of extreme sharpness results of very fine details just to get a eldery portrait with lot of character!