Soft or brittle nails may occur for a variety of reasons - normal aging processes and thyroid disease can be possible causes. In some cases brittle nails are caused by nutritional deficiencies. How is your diet? Are you eating a balanced diet? See if this help - http://tinyurl.com/yc32ka9
Not often mentioned is the fact that not everyone has long hard dagger-like nails. Many like me are born with a shorter, rounded nail, which for example will curl as it grows beyond the fingertip. Just keep them short and neat. It makes nose-picking much safer.
Have bought a 'diamond hardener', got 3 coats on, and not a jot of difference, they still feel like paper.
We have a good diet, very balanced. I suspect some of my meds, I used to have good nails.
Try rubbing almond oil in on a regular basis ferlew .Always wear gloves for household chores ,rub in hand and nail cream all the time and invest in a good nail file .The crystal one from Leighton Denny is brilliant .Buff them on a regular basis too as it stimulates the blood circulation to the nails .But get a proper leather buffer .
I would knock off the nail hardeners .A lot of them contain formaldehyde which isn't good for your nails .
Mine have been soft and bendy all my life and I am now 66. Nothing to do with health and nothing you can really do about it. Just the way you are. Keep them short as Mosaic says, and just be as careful as you can with them. Both my husband and son have beautifully shaped filbert nails which they can use as screwdrivers. Just not fair!!! I have found all the nail hardeners have ultimately made them worse. They best thing to do is use plenty of nail cream to keep them moist.