The findings come as time is running out for people to register to vote in the referendum, with the deadline for applications 11.59pm tonight.
Analysis by the Press Association found that a decisive result on June 23 could depend on whether people aged 18-24 stay at home in similar numbers to last year, when only four in 10 voted.
PA’s projection of the outcome of the referendum, based on the latest opinion polls and using demographic data modelled on the 2015 election, shows Remain and Leave currently tied on 50.0 per cent.
But if turnout on June 23 is just two percentage points higher among voters aged 55 and over, the projection changes to a narrow victory for Leave.
A one-point rise in turnout among 18-24 year-olds tilts the result narrowly towards Remain.
Almost a quarter of a million applications to vote were made online yesterday, according to the latest figures from the Government - although not all of these will be new applicants or people who are eligible to vote.
Turnout among 18-24 year-olds at the 2015 general election was just 43 per cent, compared with 77 per cent of 55-64 year-olds and 78 per cent of people aged 65 and over.
PA also found that if turnout among 18-24 and 25-34 year-olds at the referendum drops by just three percentage points compared with the general election, and all other figures remain the same, the projection of the result changes to Leave 50.2 per cent, Remain 49.8 per cent.
By contrast, if turnout among those two age groups rises by two percentage points, and all other figures are unchanged, Remain would finish on 50.2 per cent and Leave on 49.8 per cent.
If turnout rises across all ages, but by a greater amount among 18-44 year olds (10 points) than among people 45 and over (five points), the projection widens to Remain 50.5 per cent, Leave 49.5 per cent. If those figures are reversed, Leave has a narrow win of 50.1 per cent to Remain’s 49.9 per cent.
Responding to PA’s findings, International Development Secretary Justine Greening - a Remain supporter - said: “It’s never been more important for young people to get registered to vote so they can have their say. We all get one vote in this referendum and we’ll all have to live with the result - but the younger you are, the higher the stakes.
“I want us to stay in the EU so that future generations can continue to benefit from the influence and prosperity that comes from our membership of the single market. The alternative, Brexit, would see our young people’s prospects knocked sideways by an economic shock and years of uncertainty.”
People can apply to register to vote online until 11.59pm tonight at gov.uk/register-to-vote.
The PA analysis is based on the findings of every opinion poll published over the past month by BMG, ComRes, ICM, Ipsos-Mori, Opinium, Survation and YouGov (20 in total).
It uses estimates of the size of the electorate and the population from the Electoral Commission and the Office for National Statistics.