Undeveloped brains
There is a solid argument that people should not be able to vote until 25. There is more and more evidence that the brain is not fully developed until at least 25. Sixteen year olds may be allowed to drive, but their insurance rates are much higher until they turn 25.
One might argue that inclusiveness should override critical thinking ability. We don't otherwise say that people who lack critical thinking shouldn't be able to vote. However, the problem in this case is that the sixteen year old person may vote for things that a forty-six year old person might choose not to do.
Lowering the voting age to 18
The voting age in the United States used to be 21. It was lowered to 18 by the twenty-sixth amendment. One of the arguments in favor at that time was that eighteen year olds could be drafted into the army. This was a responsibility that could be imposed on someone without their consent, and at the time, without their vote. That could have also been fixed by raising the draft age, but they found it more feasible to lower the voting age.
The draft is different from most of your Irish examples, as it is a responsibility that society imposes upon adults. That gave moral authority to the argument that the voting age should be lowered to match.
Other age limits
Two of your examples related to people being punished for choices they made. In those cases, the child has made a choice to act as an adult. Even then, it is generally optional whether the child is treated as an adult. It's not an automatic result. Also, society can't prevent children from committing crimes. It can only choose how to respond. And society often chooses a harsh response, as it has found that children who do commit crimes at a young age are also more likely to do so when older.
If 16 is old enough to vote, is it also old enough to draft? Should the drinking age be reduced to 16? Should every criminal be treated as an adult from 16 on? Should we reduce the parental insurance coverage age back to 16?
Should we go farther? Some of those ages are 10 and 12. Should someone who is 10 be able to vote? Able to drink, smoke, or take other legal recreational drugs? Allowed to drive? To draft? To always be charged as an adult? Get married? To consent to sexual intercourse? To sign binding contracts?
Should we keep going? After all, there's nothing magical about the age of 10. The argument that everyone subject to the law should be able to vote on it goes past that. Decisions that politicians make today can affect children not yet born. Some of the federal debt in the US is almost two hundred years old, less than fifty years younger than the US as a country. No one alive now was old enough to vote when the debt was taken out. Yet we are still bound by it.
You skipped over one of the examples. There is no legal minimum age for paying tax. Even a newborn infant has to pay tax on any income exceeding the exemptions. So should newborn infants be allowed to vote? We could create a legalism that parents earn all money until a child turns 18, but overall, that would just complicate things. As a practical matter, we limit how children can work until they are 18.
Adulthood
In the end, it's simpler than that. We generally regard voting as an adult privilege. Driving a boat or motorcycle is not an adult privilege, so we allow children to do those things. We especially allow them to do so in places where it is not feasible to travel without driving. Perhaps we'll raise those ages in the future, to 18 (adulthood), 21 (drinking age in the US), or 25 (insurance rates drop). Perhaps we'll stop letting anyone drive on public roads and only allow computers to drive all vehicles.
Voting, binding to contracts, and joining the military are adult privileges that often go together. Prior to 18, parents make such decisions for their children. After, they can't. We expect adults to make their own decisions. The age of 18 is a compromise, but it's a natural one. Should someone not old enough to sign a binding contract be allowed to bind others to a choice by voting?
