Cannot disagree with auntiedee more!!
I have a working bred collie. A high drive one at that, they do not need to be worked 8 hours a day!
In fact, doing so will likely cause it to become overstimulated and deeply stressed.
Working farm dogs have sizeable chunks of the year where they are not working much and have to largely entertain themselves.
Additionally, when work is finished quite a lot of farmers then give the dog some quiet time to relax, otherwise the adrenaline stays raised and they become wired.
Collies become stressed and overstimulated very easily.
They need calmness and peace and quiet, if they can't work sheep then something mental like tracking or obedience is much better for them than something like agility or fly ball which done to excess will stress them out and take them over threshold.
If he is suddenly wary that could well be due to the neutering.
Neutering removed testosterone and testosterone is what gives dogs confidence.
Nervousness is NOT a collie trait!
Aloof yes, sensitive yes, nervous no.
The pulling on the clothes is most likely work drive - the instinct to stop things moving but it could also be caused in part by excitement.
Jumping and mouthing at clothes is likely excitement but if the people are moving then again, that could be the herding instinct coming out.
To fix - first of all I would teach him a good 'settle' and insist on it in the house.
Then I would look at diet as collies are especially sensitive to colourants, additives and don't react well to grains.
Most of the collie specific rescues advise raw diets for this breed as do a lot of breeders.
Food with a lower meat content can cause hyperactivity.
Then, I would continue doing what you are doing but I would also keep him on a long lead for now and as soon as he goes to jump or grab interrupt with a 'ah ah' sound and swiftly turn and walk away.
Herding behaviour applied to people can become very dangerous and needs stopping immediately.
He needs to learn that people are not under any circumstances to be herded and there will be a negative consequence for doing so.
Exercising for miles every day PLUS lots of mental stimulation is probably going to cause a hyperactive, hyper alert dog who is stressed and cannot physically relax in the end.
I have a working bred collie with a high work drive, this is a typical week for my dog....
1 walk a day, the duration varies - sometimes as short as 15 minutes, sometimes literally all day and we will stop outside pubs but on average probably an hour or two.
Sometimes those walks are 100% on lead.
Sometimes 100% off lead
Sometimes we play fetch with a ball in short bursts so walk maybe 30 mins, play ball for 5, walk 30 etc.
This is because if we play ball too long she can go over threshold and become disobedient, anxious and nippy.
Sometimes we might do a little (or a lot) training.
At home we do nothing.
That's right, nothing.
She is expected to sleep, chew an antler or play with one of her toys but if she gets too boisterous with the toy bouncing on and off the sofa for example she has to settle for a bit.
If I walked her for miles everyday plus mental training she would be an absolute nightmare, completely hyped up and unable to relax.