Well that's not true Is it?
They can go out unless they are "Vulnerable".
So what would they be doing if they could "carry on" or whatever it is you think they want to "carry on" doing?
They wouldn't be able to do anything different than what they're doing now unless all the other age groups start opening things up for them.

39% of deaths 60-79
9% of deaths 40 -59

Not an insignificant amount i would say?
Our own prime minister is what? 54/55 ish and they were making plans for his death werent they?
Remember, this is with a large scale lockdown, what would it have been like without it?
The hospitals around Cheltenham experienced 2 to 3 times more covid traffic 2 weeks after the festival, as did liverpool after the CL game.
That's akin to what would happen if we were to release lockdown too early.

Your original statement IMO implied that the majority of over 70s wanted to go out no matter the risks (and you used your parents as an example).
My 70+ aged uncles and aunties, the Bowlers and plenty more I've spoken to accept that even though they may "want" to go out, it isnt the best thing to do yet.
And unless they let all the 60 plus age group out and keep the under 60s on lockdown then it wont be safe for them. Because the ones who arent dying are still passing it on to those that statistically may.

All sorted.
You can sit on park benches and go back to work if you oil your bicycle chain.

The country has been asking for a plan, they now have it, with conditions.

The Tories love bicycles.

They've ordered a million cycling high visibility vests from Turkey.
One hole to put both arms through.

Although nobody can go back to work because their employers havent been given time to prepare for the "unknown".
There is also a problem now, with the 4 parts of the UK all having slightly different rules for their people, which becomes magnified for anyone living in, say, Wales but, working in England.

There is devolved government, which in may ways is a good thing but, for the Covid19 situation, it may have been helpful to have a UK wide policy ?

I got the impression it was more to do with reducing the cost to the government by those on furlough returning to work even if the businesses are not yet ready.

Once again, the new "plan" seems half baked and not properly thought through, not to mention the different parts of the UK now working at slightly different speeds.
There is no doubt that the nation is haemorrhaging money at a huge rate and that somehow, a way has to be found to unlock the ecconomy but, I'm not sure this is it, although, it's worth noting that a number of countries are already having to tighten their new slightly less stringent rules.
It's one hell of a conundrum.

More employers shut down originally than expected. Hence the change in 'branding' from stay at home to stay alert. Let's get the economy going, whilst keeping people safe. Behaviourally we now understand social distancing, that hasn't changed, let's get it into the workplace.

As for the variation in the 4 countries, just do what they say in the country you live.

The first part "may" be possible for some employers / employees but, definitely not with 12 hours notice ??

The second part is a little odd/impossible with absolutely open borders between England / Scotland and England / Wales

If you live in Wrexham and work in Chester or visa versa, what are you permitted to do ?

Also, in theory, you could drive into Wales to go walking (from Wednesday) but, in Wales itself, you are supposed to stay home ??

These are just a couple of examples

The new "rules" are as clear as mud

Who said work must open tomorrow? Some companies have been planning to reopen for weeks. The option is from tomorrow, not Tomorrow, but given the other minor examples you have provided, playing on words is the basis of your mantra.

The only thing that has changed is that you can sit in the park. You just worry yourself with that.

Here's a quick factoid about what secondary schools reopening, with social distancing measures, would look like.

At the school where I'm based, we have 360 kids per year. The suggestion is that just year 10s will return in June to get some time with teachers before next year's exams. If this is the case, and the 2 metre social distancing rule has to be observed, the dinner queue would be nearly half a mile long. Obviously, they'd use the three sittings to be able to spread out the dinners, but you're still looking at 3 sittings, each with a 240 metre long queue.

There's a fair bit more to worry about than sitting in the park but, if that is your priority, knock yourself out bud.

I think his words were "you can go to work tomorrow" ??

No forewarning for businesses to prepare, let alone the kids are still at home, no sense really on how people will get to work but, apparently walking or on a bike are now preferred.
Did they really need the extra few days from Thursday to come up with this "plan".

We would have been better placed keeping the "stay home, protect the NHS, save lives" slogan but, saying that those who could travel to work safely and whose employers were prepared (difficult without government advice) should start to go back to work, with the obvious caveat around vulnerable people and for me, the plan MUST be UK wide.
Its quite ridiculous having different advice in Scotland and Wales, to the advice being given in England.

All seems fairly straight forward to me. You will get more detail today from Boris in Parliament and in the daily press briefing.

Boris clearly said go to work in your car, quite clearly said that, but you must have missed that bit as your were checking the brakes on your bike.

Sturgeon has been playing games for weeks. Releasing national information in advance of the UK, engaging with the Scottish public regarding a phased opening, then pulling back. Sadly she's politicising this which isn't good for anyone.