Hi LNM,
Getting back to walking will be slow, but steadily progress. Sometimes it's a week on crutches and then just keep them handy. Other times it’s a month then a cane for a bit. It is also not unusual to require pain medication at this stage. He should ask the doc about that and not be afraid to call in if necessary. There are a lot of factors. Anything that was injured initially will still be healing: heel pad, subtalar joint, tendons, and other foot parts. Great ROM without those hurting now is a good sign. Still, the non weight bearing time will have taken a toll. The Achilles tendon will have shrunk some. Circulation, flexibility, muscle tone and even general stamina will not be up to the demands of regular walking. It might be a lot more comfortable to use the boot at first, working on weight bearing and locomotion, followed by foot and ankle strength and stability sans boot. It seems to be automatic to dump the boot when it becomes more trouble than it is worth, so don't worry about that. Ditto for medications.
Those who were the most active pre-injury seem to bounce back quickest. Partly because of the condition they were in but also possibly because of the amount of effort they were willing to put into recovery. How far he can get at first isn't important. For some it is "Whoa" on the first step. What counts is doing more of what ever he can so he can build on that. If he manages 10 steps he could do that throughout the day. When he can get around the block, he should extend the distance next time. There's one snag: 2SF1SB. That's two steps forward, one step back meaning there will absolutely be times when he over does it and needs a day off. Rather than being disappointing, this should indicate to him that he's not being a slouch.
PT is great and essential. Don't let him quit until he is walking with a proper gait (no limp). While PT is good because they are specialists on the subject, I would recommend that he at least match the formal effort with real world activities - on stairs, carpets, outdoors and any environment he will be returning to. It's also a good idea to keep up with the range of motion exercises because the limited amount of walking at first won't be contributing to that.
The next three months could result in as much impatience as I'm sure characterized the previous three. When he says: "I can't do 'A'." take note. Then later when he says: "I can't do 'B'." remind him that last week he couldn't even do 'A'! There will be 'new' pains until the foot bones get comfy again, especially at the very top of the foot. The same goes for the scar tissue at the surgery site as it works free again and from the swelling that seems to take forever to disappear completely. Don't let those all be a worry, but don't hesitate to check with the doc when in doubt.
TC