GERRY Adams and the Sinn Fein leadership are being accused of showing a lack of respect to the new constitutional think tank by not bothering to show up to its first proper meeting.
The Convention on the Constitution decided to recommend reducing the voting age to 16 but wants the presidential term left alone.
The proposals will go back to the Government, which can decide to accept or reject within four months.
A recommendation that is accepted will go to a referendum.
The members voted by a narrow margin of 52pc to reduce the voting age.
The convention also voted against reducing the age of candidacy and also against reducing the voting age for some types of elections.
Members also voted against reducing the presidential term, by 57pc to 43pc.
The convention was overwhelmingly against holding the presidential election on the same day as the local and European elections.
The members also voted by 94pc to 6pc for citizens to be given a say in the nomination of presidential candidates and for reducing the age of presidential candidates from 35.
The convention is made up of 100 members – 66 ordinary members, 33 politicians and an independent chairman.
Members spent the weekend weighing up the pros and cons of the first two items on its agenda.
The convention will sit for eight weekends over the course of the year.
Sinn Fein was the only party to send an entire team of substitutes to the first proper meeting of the body.
Fine Gael group leader Charlie Flanagan said he felt it was important parties "would put their best foot forward" for the convention and treat it with respect.
Sinn Fein's official members of the convention, Mr Adams, Martin McGuinness and Mary-Lou McDonald, were not present, and the party sent two senators and a member of the Northern Ireland Assembly in their place.
Mr Flanagan said to only send substitutes showed a lack of respect for the body, particularly for the first meeting.
Sinn Fein senator David Cullinane, who was one of the substitutes, said the party leaders "will come" to later meetings.
He said the party was sending different representatives to meetings, depending on what issue was being debated.