What wines does your dad like, generally speaking, some wines do tend to be stronger, so if he's looking at New World, they will tend to be stronger, for reasons I mentioned in my previous post about wine strength.
I'd say something like a Pinot Noir, Gamay or Grenache might be lower alcohol than what he's been drinking, but they're probably going to be lighter-bodied than what he's used to.
Because it's a balancing act and the stronger alcohol level acts as a counterfoil to full-bodied elements in a wine. If you drank a medium or light bodied red wine that had a high alcohol level, it would be out of whack, similarly a full-bodied wine with much lower alcohol levels would be out of balance.
So if he's looking at bottles of the same style of wine hoping to find one of lower alcohol level, that's probably not going to work, he's going to need to look at different styles (country/region/grape varieties), maybe more Old World, like the ones I mentioned before, or maybe a younger Tempranillo or Garnacha, steer clear of fuller-bodied Crianza, Reserva, Gran Reserva, or a Merlot rather than a Shiraz.