Despite this, net use among this group is growing with the numbers trying the net doubling since 2011, it found.
It also revealed that 25% of disabled people have yet to use the net - a figure campaigners called "shocking".
About 88% of all UK adults, about 46 million people, used the net in the last three months, it said.
The ONS bulletin on net use in the first three months of 2016 revealed that 91% of people living in London went online regularly. By contrast, in Northern Ireland only 82% of people are regular users of online sites and services.
Pete Lee, from the ONS's surveys and economic division, said the statistics revealed some significant changes in usage and exposed those sectors of the population where net use remained low or patchy.
Net use among women aged 75 and over had grown by 169% since 2011, it found. However, it found that a significant number of older people who start using the net did not do so consistently. About 5% of those aged 75 or more had stopped using the net in early 2016.
"While we have seen a notable increase in internet usage across all groups in recent years, many older and disabled people are still not online," said Mr Lee.
Mark Atkinson, chief executive at disability charity Scope, said it was "shocking" that 25% of disabled people had not used the net as it created a significant digital divide.
"Digital access has the power to make life cost less," he said. "Many people go online to compare the best consumer deals and offers."
"Life costs more if you are disabled, from higher energy bills to specialist equipment. Scope research shows these costs add up to on average Â£550 per month," he added.

Replacement schemes would be discussed with colleagues after last month's vote to leave the European Union, he said.
Mr Eustice previously said that Welsh farmers would get "as much support" as currently if the UK left.
Under the EU Common Agricultural Policy Wales receives Â£250m a year in direct payments to farmers.
That is in addition to more than Â£500m between 2014-2020 to run a rural development programme.
Mr Eustice  was speaking to BBC Wales at the Royal Welsh Show, in Llanelwedd, Powys.
"What I can guarantee is that...once we leave the EU, we won't be spending that budget on EU membership, and the things that currently we delegate to the EU we will be funding ourselves," he said.
"The point I'm making is that now we have a new government in place, before we can guarantee exactly the same amount of money, that is a discussion we've obviously got to have with government colleagues.
"I can't do it at the moment, but it doesn't mean it won't happen."
He added: "Clearly we need to have the time to have these discussions and to work out what we're going to do and how we're going to do this negotiation, what the time frame is, and then how we're going to fund policies going forward."
Mr Eustice, who campaigned for Leave, said he was clear through the referendum campaign "that when you take back control for a policy and take back control of it on things like agriculture...with that comes a responsibility to get it right and to fund it properly.
"That is the case that I will be making, and I'm confident that will be the position that the government adopts."
Earlier, the Welsh Government's Environment Secretary Lesley Griffiths has said that Brexit was an opportunity "forge a new, distinct path for Wales' farming food and environmental sectors".
But Welsh Conservative leader Andrew RT Davies warned ministers in Wales lack the capacity to make Wales-only agriculture policies after Brexit.
Mr Eustice said: "What we've got to work out is a UK wide framework for an agriculture policy.
"There will be issues such as international trade that will obviously be done by the UK...
"What I'm keen to do is have as much discretion as possible for individual devolved administrations to pursue what they think is right for their own agriculture.
"I see a situation where the Welsh administration will have far more power than it has now, but will still need to have some kind of UK wide framework to prevent anti-competitive policies getting in place."
He said he wouldn't want to have "distorting subsidies in place that affected one area more than another".
He said "broadly" Westminster would be in charge of agriculture cash, with the Welsh Government given its share, but with more "discretion" for Wales to spend the money in the way it likes.
Almost two-thirds of people aged over 75 have never gone online, suggest figures from the Office for National Statistics (ONS).
[NEXT_CONCEPT]
UK farming minister George Eustice has said he cannot guarantee that future agricultural support programmes will be as generous as current EU subsidies.