My mum developed FTD as a result of a head injury she got in a cycling accident that happened when she was on a cycling holiday in India when she was 66 (so had obviously been really fit and healthy). Essentially the healing process didn't stop and because destructive
. She was diagnosed at 69
.
The early forms are usually "rapid onset", which is actually a saving grace. She went into a home not long after her 70th birthday and died shortly before her 72nd birthday.
Every dementia is different. In mum's case, she never forgot who we were, nor did she lose her memories - although laterally I got the impression that she couldn't be bothered remember. What she did lose was her language skills (she'd been an English teacher) and her love of music, which no longer meant anything to her (so it annoys me when some people say you can "always" reach dementia sufferers with music 
). Towards the end she could barely talk and she also lost the ability to balance or walk (but couldn't recognise this, so would try to get out of bed or her chair
)
I wouldn't wish it on my worst enemy. I visited her regularly - 2 or 3 times a week, as did my dad and many of her friends. We made sure she had at least one visitor a day.
Dh could always tell when she'd been "better" when I visited as I'd come home more upset, having had a glimpse of the wonderful vibrant woman she'd been 
.
She hated it in the home, even though it was a good and caring place. My dad never stopped loving her but knew he couldn't cope with her at home.
Towards the end, I commented to my dad why we were bullying her to eat: it was the one thing she had control over. It meant that every time we visited, we were stressed as we tried to make her eat some yoghurt or grapes or something else high calorie. We stopped doing that and concentrated on mouth care and fluids and she died a few weeks later.
My aunt (my dad's sister) gave me the best boy of advice. Their dad had died of a brain tumour when they were in their early 20s: my dad had to return from Uni where, although he'd got his degree, was going to spend a year as the President of the equivalent of the Student Representative Council, to run the farm). She told me that it would take time - at least 6 months - but that eventually I would be able to remember my mum "properly", as the wonderful vibrant woman she'd been, rather than the husk she'd become at the end. I held on to that bit of advice and it helped - although it took me closer to a year to forget the image and character her during the final year and a half.
It's been 10 years now since she died (16 years since her accident and 13 years since we realised that the progress that she'd made - about a 80% recovery - was going backwards. I can now remember with happiness and know that she helped me become the woman that I am. I still miss her - especially sharing landmark moments like taking ds to Uni and his graduation - but it doesn't hurt so much. But don't beat yourself up if you tear up when talking about her - that's part of your love for her and the memories you share (it's taken dh a long time to come to terms with the fact that it's not that I'm upset - I'm just emotional and that ok).