The law is named after former Dundee United footballer Frank Kopel, who was diagnosed with dementia aged 59 and died six years later aged 65 in 2014.
At the end of his life his family was paying about £300 a week in personal care.
His widow, Amanda Kopel, who campaigned for the law, said she knows people who have died waiting for the financial help promised by the change in legislation. The law was brought in by the Scottish Government in 2017 following sustained pressure by opposition politicians and campaigners, but ministers decided to introduce the changes from April 2019.
Those campaigning for the law argued it should be operational from April 2018, preventing hundreds of patients from having to fund their own care packages.
Now, analysis of ISD Scotland statistics shows that at the end of March 2018 there were 867 people in Scotland under 65 being treated for dementia.
Of these, 484 were aged between 60 and 64, 245 from 55 to 59, and 85 from 50 to 54. A further 38 were aged between 40 and 49, and 16 patients receiving dementia medication were 39 and under.
Mrs Kopel said: “There have already been under-65s who were denied free personal care because of the repeated excuses about why Frank’s Law couldn’t be implemented until April 2019.
“I realise the wheels of government can turn slowly, but if things had been put in motion long before 2017 by the SNP, and if it had taken the issue seriously, Frank’s Law could have, and would have, been delivered long before now.
“How can you put a price on a person’s life? Sadly, that’s exactly what the SNP has done, but churning out excuse after excuse as to why it wasn’t feasible or affordable. I know there have been many people under 65 who have sadly passed away since the announcement in September 2017.
“They were living in hope, and I am saddened for those who were unable to hang on to see this come into place.”
Scottish Conservative health spokesman Miles Briggs added: “The SNP was dragged kicking and screaming to agree to bring in Frank’s Law.
“As soon as the legislation was passed it should have been brought in at the next reasonable opportunity, which would have been April 2018.
“Instead, the nationalists dithered again, and as we can now see that means that hundreds of patients missed out. These figures clearly show that, in 2017/18, more than 800 patients aged under 65 were being treated for dementia in Scotland.
“At least if the SNP government had moved swiftly, those people could have caught a break by the time April came around. But for many, the SNP’s needless 12-month delay will have been too late.”
A Scottish Government spokesman said the extension of free personal care would be fully implemented by 1 April, 2019.