At least 35,000 young people have not registered to vote in the Senedd election on Thursday (6 May).
This will be the first time that 16- and 17-year-olds are able to cast their vote in a Senedd election.
However, figures collected by the BBC indicate that as many as 54% have not registered to vote.
This compares to 76.7% for the population at large.
In Bro Morgannwg, 68.6% of 16- and 17-year-olds have registered to vote, while only 31.7% have done so in Abertawe.