The infinity engine games are all turnbased behind the scenes, but I do not know if they all can be set to totally turn based (that is when they pause after every combat turn)
I have all infinity engine games so I could check but I'll give you a list of the ones I know 100% sure:
- Baldurs Gate I and II (BG I can be put into BG II using
BG1Tutu)
- Icewind Dale I and II
- Fallout I and II
I'm not sure if planescape torment and the original BG I (not placed into the BGII engine) can be fully turnbased.
The turnbased means that you set the game to autopause after every combat turn, everywhere else it will be real (compressed) time but in general these games have nothing against the clock (as far as I can remember, there is sometimes that you have to get from point A to B in a week gametime but that's most of the time very generous since you just have to travel there)
Now these games might be a bit old (they ARE a bit old) but they have a nearly unsurpassed storyline (Star Wars KoToR is close if not equal in terms of story) and will get you hooked.
If your dad loves roleplaying and interaction between different people i'd reccomend the fallout series and the BG series.
Planescape torment is also a fantastic RPG (the best imho) but it's incredibbly tough, you need to be quite smart to see the solution to many puzzles and riddles.
if your dad would prefer some more action i'd reccomend icewind dale, it's also an RPG and you also have interaction between externals, but you design your entire party of 6 so there's no interaction in your group of players that you control.
I think most of these games can be found in the bargain bin or online (the really old ones like Fallout 1 and 2 and BG I are rather hard to find)
Now for something completely different:
Space Empires IV:
which can be found here
http://www.malfador.com/
Is an exellent turn based space strategy game, but it's not an RPG (you can roleplay in it with other players, but it's mainly a very tough strategy game)
I hope you find something your dad likes.