Is 76 too young to put mom in a nursing home? I need help :(

This woman has dementia (horrible to deal with and impossible to reason with them) and physical problems. Apparently her behavior is having a terrible negative effect on you and your family. You have a family and a life to lead and you have the right to have peace and do what you need to do. The minute the behavior of these people starts to have a damaging impact on you and your family and you cannot stop their bad behavior, the you must face the fact they cannot remain in your presence. They must be placed. That time is now - she has dementia and you should NOT have to deal with the impact.

There are people in their 50's with early onset dementia that have to be placed.  Do not feel guilty.  You have every right to feel sad about the situation, but there is no reason to feel guilty.  You and your family are entitled to a life outside of caregiving.  Find her a safe place to go, hopefully close to your home so that visiting isn't a problem.

Take care of yourself.

Just did it with my mom who is also 76. It is horrible right now because we can’t visit normally due to Covid but trying to work from home, care for her and my marriage when we are all stuck in the house was horrible too. It became unsafe for her - she has hallucinations from LewyBody dementia and thinks people are breaking in then has panic attacks. But I don’t have guilt. I know I did the best thing for all of us. But do prepare yourself because you will go through all the stages of grief after. Take a few days off work if you can.

Age is not the criteria for nursing home placement. Medical need is the criteria and it sounds like your LO has reached that stage. It is particularly true is her actions are affecting you and your family's relationships. You are not a trained nurse or CNA and you don't have the resources to keep her safe.
As has been mentioned, get all your legal ducks in a row if they are not there already. If you have any questions or need help please invest in a good certitied elder care attorney; they are worth the money.
Placement anywhere is difficult in the midst of the raging pandemic. If your mother is not able to private pay for placement, she will need to have Medicaid which you can apply for. Be aware that Medicaid beds in AL MC are few and far between and are often given to those residents who have been private pay for years. Many NHs have secured MC units but most will require a legitimate payment source prior to admission so that is why you really want to get the Medicaid application going as soon as possible. I suggest you contact your state or country Office on Aging for more detailed information. The social workers there will probably know which NH are accepting and will guide you through the Medicaid process. Good Luck