I understand, and totally agree, with what you are saying. But, for the purposes of this thread, let's forget about revenue limits, affordability and current tax rate (as there are already a lot of threads covering the exact details of tax relief, affordability ans revenue limits).
Let's just suggest a percentage of salary that you should have invested at age 30 in order to reduce contributions to 10% and end up with a reasonably good pension.
If, for example, you were to say 105% of salary, this figure is achievable by contributing 15% per year from age 23 (assumming no gains in the underlying investments and no rises in salary levels). However, as there should be gains in the investments, the figure should also be achievable if you started after 23.
For this thread, we don't need to discuss details of how to achieve the target - just what that target should be.
Personally, I think the suggestion above is quite a good one to go by (if the age/2 contribution level is a valid rule of thumb). However, other people's opinions may vary.