I might just have been lucky with clients when I actually guided back in the day.
Well you were "lucky" with me. I took a lesson from you in the Gunks on How to Lead, and it worked so well that I never took another lesson in leading. The format of that day surprised me, because I had to recruit my sister as a belayer. I have no idea what climbs I led, or or what moves you were doing -- I guess I was so focused on the learning.
I remember I chose you as a guide because I'd found out you were a mathematician. In the last couple of years I've done lots of climbing with a mathematician who is about the same age as the father of the OP of this discussion. He didn't start climbing until after he turned 50. Now he leads hard 5.9 in the Gunks. Last year I belayed him when he led his first 10c (sport) - on sight. I was thrilled to be a part of his success (and glad that I didn't have to lead it myself). His immediate unconsidered response was: "Yes but I rested on the pro" - (one time, after making a strenuous clip)
I hope I can be disappointed in that special way when I turn 70.
P.S. You know there is a "third" pitch to Casa Emilio, which is interesting and fits the 5.2-5.3 difficulty of the route (but perhaps not for beginners because it has a traverse). Worth knowing about if making the long walk out there.
I tried Crimson Corner and stuff around it today. Going up and down the arete itself in the obvious way was not as dirty or licheny as I remembered. I'd call it OK slab climbing. No arete-specific moves. So if you want 5.1 slab climbing with an easier approach than the "Practice Rock", there it is. (not very representative of the great 5.2-5.4 climbs of the Gunks).
Explored various other short sections off to the sides of the arete which I suppose could by tried by those looking for "something more". The chimney to the left of the arete didn't seem to have much to offer (for me anyway).
I think I sorta did the "Yale" route, listed as 5.4 in some guidebooks. To me it seemed like an athletic 5.5 move near the bottom followed by decent 5.2-5.3 face climbing above. (? perhaps could give less athletic climbers a "boost" so they could enjoy the easier climbing above ?)
Dirty Chimney I still like. I noticed that the upper (dirtier) section (which I assume almost nobody ever does) has a tricky exit move, perhaps 5.2?
definitely the ABC Slab... it's sometimes used by guides for groups, but it is usually open. It follows an approach tail at the beginning of the Uberfall. It's easy slab with a bunch of trees above it... Probably goes at 5.0-5.2 depending on the variation... but it is at the top of the cliff giving a great view.
"ABC slab" sounds like another name for the "practice rock".
Or please correct me on that.
So I think it's more helpful to say that it's near the beginning of the Undercliff road (above left).
The advantages of the "practice rock" slab over the Crimson Corner slab are: more different lines to climb, perhaps a nicer view. There are some lines by the practice rock with some non-slab moves (as there are with Crimson Corner). And the Practice rock is much closer to the parking lot -- but definitely farther from the real Gunks climbing scene.
If the OP's father has done some indoor gym climbing, I would not be so confident he "will love" slab climbing. I don't love slab climbing, and I don't know many climbers who do.