Not ASAP for sure. In the case of Mars, possibly never to the surface, depending what we find, though to orbit could be done at an early stage.
For the Moon, there aren't that many issues with sending humans there. Main thing is that we have a golden opportunity right now to study the lunar atmosphere. It has a very thin "atmosphere" where the atoms are mainly ballistic, hardly hit each other. Yet we can learn a lot from studying it. For instance if there is ice at its poles - where does it come from? Does it come from Earth's geotail of water vapour - or from interplanetary space, or from comet collisions on the Moon for instance.
Because the atmosphere is so thin, then if you land humans there, the rocket exhausts would totally overwhelm the atmosphere, making these studies very difficult.
Right now, it's several decades since the lunar landings, apart from the Chinese one of course, but that didn't have a huge impact on the lunar atmosphere. So it is an ideal time to do this study.
We could also have rules about the type of propellants used for landing on the Moon and taking off again. Not much propellant is needed because of its low gravity and as you can see from the size of the lunar module. If you can use low mass fuel such as hydrogen and oxygen rather than heavy mass solid propellants, then that dissipates more quickly so has less impact on the lunar atmosphere.
Apart from that - well the surface of the Moon is large, and any contamination the astronauts bring will be localized to the landing spot - since it has no winds or dust storms to move it about.
There are no regulations currently to stop you landing anywhere on the Moon. But some places may be sensitive to humans, e.g. the ice at the poles, might want to keep some of it off limits so that it can be studied in a pristine state.
So in the case of the Moon ASAP is fine except for this suggestion that we should do robotic studies of its atmosphere before we land rockets in a big way, and avoid use of heavy molecule fuels. And some areas may need protecting. It's also been suggested that historical landing sites need protection, that you can't just land next to the Apollo 11 landing site and walk up to it, walk over their footsteps etc. Some kind of exclusion zone around the first landing sites for historical reasons.
In the case of Mars though it's much trickier.
Even for its moons Phobos and Deimos - they are rather small, just a few kms in diameter. Humans walking over them would probably cover the entire surface in footprints and the ISS dumps tons of material to Earth's atmosphere every year, so a human settlement anywhere would surely have a large garbage heap next to it within a year or two of occupation.
I think it's best to have experience of human missions to the Moon before landing on Phobos and Deimos to get an idea of how much impact humans have on places they visit for long term settlement, and whether there are ways this can be minimized.
For Mars surface, then it's an interconnected system with winds, and global dust storms that cover the entire planet. So though it's been suggested that humans would only contaminate the part they land on - I'm dubious about that myself. Carl Sagan first brought this up. He pointed out that the iron oxides in the dust storms are very effective at screening out UV light and a microbial spore imbedded in a dust grain could be carried anywhere on Mars in the hundreds of miles per hour winds.
So, I don't see myself how a human habitat, complete surely with big garbage pile eventually larger than the habitat itself in mass, can possibly keep its contamination by Earth microbes to just the landing site - unlike the Moon where this is definitely possible.
Of course we don't want to introduce Earth life to Mars since the objective for going there, one of the main things we want to do, is to find out if there is any present day or past Mars life. And the surface is no longer thought to be sterile as was thought a decade ago. There are now numerous ideas for possible habitats there, which have to be investigated, and much of it is already classified as "special regions" where life is possible on the surface, or at least, has not yet been ruled out.
So - I can't 'see COSPAR passing a human mission to Mars surface, especially taking account of the possibility of a hard landing on an unintended site on Mars, leavaing astronaut bodies, food, water, air, scattered across the surface to be spread in the Martian dust storms. The strong winds can only pick up small grains the size of cigarrette ash. Most stuff would just stay where it feel but there would be many opportunities for microbial spores to spread after a hard landing.
And Mars life could be very vulnerable to Earth life - it could be tough, but coulud be vulnerable. For example if it is some earlier form of life, say only RNA based and using ribozymes instead of ribosomes - tiny cells maybe as narrow as 10 nm in diameter - well such life doesn't exist on Earth any more (unless those are right that say it survives as nanobes, a minority fview). So presumably DNA based life made it extinct. So same could happen on Mars before we have a chance to study it.
If we do find something as interesting as that on Mars then some astroibiologists at least would say we have to leave Mars to the Martians, even if only microbes, and study it only, and remove all traces of our contamination when that's practical.
So - landings on Mars should be biologically reversible until we understand it better. But it's a little hard to see how a human landing could be biologically reversible.
Instead we could send astronauts to orbit to study it.
Or we could study it via robots from Earth. I don't think there has been a careful comparison study but we might send humans anyway because of the human interest.
As well as these issues, there are issues with achieving a closed system, or reasonably closed system, reducing need for supply from Earth every few months as for the ISS, and also developing systems reliable enough to last for years without the ability to supply replacement parts from Earth as so often happens with the ISS. So those are practical reasons to do it not quite ASAP.
Can only really be sure that a system will work for the entire multi-year mission by testing in previous multi-year missions around Earth.
So could do multi-year missions to the Moon reasonably safely. Get back to Earth within a day or two rather than a few hours for case of ISS.
But it might be that it's only really safe to go to Mars after we've done a few of htose multi-year missions to the Moon. So that would mean a decade or so after the first multi-year missions to the Moon. Unless that is that we find a way to get to Mars and back in just a few weeks or even days.
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