Here are a couple of reasons to vote yes or vote no in the 'second referendum'. More analysis is below.
On May 22nd the second referendum asks us whether the Constitution should be changed to allow those over 21 run for President? The current threshold is 35. The Constitutional Convention agreed by 50 to 47 (with 3 abstentions) to put the motion to the people. But is Ireland an outlier in putting the threshold at 35? The evidence suggests not. Across European countries with similar political structures, there are big differences, as seen below.
Eligibility for Parliament Eligibility for Presidency
Croatia 18 18
Estonia 21 40
Germany 18 40
Italy 25 50
Ireland 21 35
Slovenia 18 18
So with such broad distinctions across countries, how do we choose to vote yes or no?
Here are a couple of angles in favour.
Firstly: the limit is arbitrary. What’s so important about 35? Maybe you have a car, a mortgage, or a child? But why do these things make you suitable for the presidency? Under 35, you can become a TD, a Senator, a Minister, a Taoiseach, a doctor, a dentist, or a judge. All roles that have arguably more responsibility than that of the Presidency. So voting yes is about equality.
Secondly: the debate is misguided. This isn’t a referendum to elect a 21 year old president. This is also a referendum to allow 33 and 34 year olds to run for president. Do you reject it because you disagree with a 21-year-old president? In that case, then you can simply not vote for that 21-year-old candidate. So voting yes is about the free market for the presidency.
And thirdly: lowering the limit is about future generations. Younger presidents will live longer and so are more invested in the future and can represent future generations. This is shown below using a life expectancy of 81 for the next presidential election in 2018.
Years Remaining in 2018 Expected Death
Current Limit 46 2064
Limit under Yes vote 60 2078
As can be seen, changing the limit would mean the president can expect to live to 2078 and not 2064 and so has more of his or her future to think of.
But let’s look at a few arguments against.
Firstly: maybe the age limit is out of date? Instead of lowering the limit, we should increase it, to keep it in line with what the drafters wanted. Life expectancy is rising and 35 is not what it used to be. When the constitution was written in 1937, life expectancy was about 59. So by 35 you only had 40% of your life left. That’s the same as a 48 year old now. So voting no is about staying true to the constitution.
Secondly: we cannot risk unprepared presidents. A younger president may not be ready. He or she may be reliant on the party, may lack experience to decide, or may lack the confidence to lead: all of which would lead to crises. Voting no is about keeping market regulation tight.
And thirdly: voting against this makes scientific sense. Are you mature enough between 21 and 35 to be a responsible president? New research means “scientists can now demonstrate that adolescents are immature not only to the observer’s naked eye, but in the very fibers of their brains”. Some psychologists are saying adolescence runs up to 25, and some are saying the mid-30s, because only then is the frontal core – “the part of the brain that makes us human“  – able to deal with planning, memory, and impulse. So voting no is about scientific evidence.
So clearly there are strong arguments in both directions.
Do we think the limit is arbitrary? Or do we listen to the drafter of the constitution?
Do we believe in 34 year old presidents? Or do we risk unprepared presidents?
Do we feel this is about future generations? Or do we believe in the science?
But all of this boils down to two things. Lowering the limit will leave the election decisions to the market. Keeping the limit as it is would prevent the market making mistakes. So this referendum is about your belief in the free market for the presidency, or your belief in very tight regulation of that market.
 Women and Men in Ireland, CSO 2013
 *“– American Medical Association APA, American Academy of Psychiatry and the Law, American Society for Adolescent Psychiatry, American Academy of Child & Adolescent Psychiatry, National Association of Social Workers, Missouri Chapter of the National Association of Social Workers, and National Mental Health Association. Brief of amicus curiae supporting respondent, Roper v. Simmons, 543 U.S. 551 (No. 03-633). 2005.
 Wallis, BBC Magazine, 23 September 2013
 - Sowell ER, Thompson PM, Holmes CJ, et al. In vivo evidence for post-adolescent brain maturation in frontal and striatal regions. Nature Neurosci. 1999;2:859–61
 Prof. Blakemore - Edwards, PhysOrg.com, 22 December 2010