Jimmy Carter is still “emotionally engaged” as he approaches his 100th birthday, according to his grandson Jason Carter.

The longest-living former US president in history, who entered hospice care in February last year, is set to celebrate the milestone on October 1.

“He’s been in hospice for over 19 months now and he has really physically diminished”, his grandson told People magazine. “[He] can’t do much on his own.”

“But he is emotionally engaged and still having experiences and laughing, loving.”

In June, Jason admitted there had “really been no change” in his grandfather’s condition since he went into hospice in his native Plains, Georgia.

In November last year, Carter’s wife and former First Lady Rosalynn Carter died in aged 96, just months after being diagnosed with cancer.

Speaking to Southern Living, Jason said his grandfather was “experiencing the world as best he can as he continues through this process”.

He added: “After 77 years of marriage … I just think none of us really understand what it’s like for him right now.

“We have to embrace that fact, that there’s things about the spirit that you just can’t understand.”

Although Carter isn’t awake every day now, his family still visit frequently.

Jason recalled one visit earlier in the year when he asked his grandfather how he was getting on.

He said: “I told him, I said: ‘Pawpaw, you know, when people ask me how you’re doing I say, ‘honestly I don’t know’.

“And he kind of smiled and he said ‘I don’t know, myself’. It was pretty sweet.”

– with AAP.