The thing you need to realise is that age is not really the problem. Yes, it appears to be the problem but it isn't. It is just one more way God helps us to discern. I am 60 years old and have been actively discerning for the past 6 years, since I was 54. There have been communities that have told me I am too old for them, communities that others have told me accept older vocations - and at first I wondered why they would say no to me and not to someone else of the same age. Over time I have come to realise that God uses a variety of ways to guide us into the place He has prepared for us, and this includes our age, our health, our country and/or language, etc. And sometimes there are other factors that affect a community's decision, but all of these are simply tools that God uses for our good.
First, get to know yourself and what attracts you to specific expressions of religious life. For example, you say that you now feel an affinity to cloistered life. So what about cloistered life attracts you, and in what way? Is it the poverty of Poor Clares? The contemplation of Carmelites? The hospitality of Benedictines? WOrk your way through all of the cloistered charisms - there are many. Ask if you want a newer community or an older one. You get the picture.
Then, discuss all this with a spiritual director - an experienced one, and preferably one who knows a little bit about religious life from either having lived it or studied different ones. Don't try to find all the answers online or through forums. Pray a lot and ask God to guide you - discern the workings of the Holy Spirit within your soul - because God is directing you in this very important life choice. If you aren't sure of the spirituality or charism then it might be time to visit a few places (without mentioning to them that you are discerning at this stage - this is just the investigation to help you understand your own spirituality).
Finally, when it is time to get serious (and this could take awhile), spend a little time with a particular community, getting to know them from the outside. There are different ways to do this. And you can write to me via email if you need more help with this. sponsajesus at gmail dot com.
The reason I advise this path instead of just flooding communities with letters saying, 'Hi, I am old, do you take women like me?' is that I have done it (well, maybe not exactly in those words but you get my meaning) and it doesn't work well. God can still use this approach, and has done so for me despite all odds, but it isn't the best way. Think about it. If you wanted to apply to a college or university, you put a little thought and time and research into it before actaully applying (well I did anyway). Not only do you have to be acceptable to them, but they have to be acceptable to you. Otherwise, the 'marriage' might not last, and you will end up outside again, wondering what happened and feeling like a failure no matter how hard you tried. And you will always be a failure in some people's eyes anyway after that. I can't tell you the number of nasty comments I have received from so-called 'nice' people who have kindly explained to me that I have no vocation because I wasn't able to persevere in a really abusive situation. Nevermind. We move on. But if you can find your home the first time out - so much the better. Trying to keep doing this discernment stuff 5 or 6 years down the track isn't as easy as it is when one first starts out. And every year is another year older...
And a fact of life - it IS hard for older women in religious life. It is also hard for younger women in religious life - for different reasons. But for each age, there are things that are difficult and things that are easy. Your age is just one of the factors so don't let it become the focus of your discernment.
So why do I say it isn't about age? Because it's about God. If He wants you in religious life, and if you don't give up, then it will happen. The trick is to determine if it is a real call or not, and only you can do that. But if you are sure, then what it takes is that same thing that it takes to succeed in religious life, a deep and personal love for Jesus and a commitment to keep trying as long as is humanly possible. But essential to that commitment is being in the right place, the place God has prepared. If you find your home, then everything will contrive to help you in your vocation, most especially your sisters. A real religious community is full of love and mutual upbuilding, helping each other to live in God every day. I warn against entering a community just because they accept older women - there is more involved in this that just finding any place that will take anyone.
Ok, so maybe I sound preachy here - sorry if I do. I'm just writing from years of experience in actually living in the trenches. You will, no doubt, have to have your own experiences and fall down a few times and get up again. But I just wanted to let you know it is possible. I will certainly keep you in my prayers and ask God to guide you in the direction of the home that He has prepared for you. But please believe me, it isn't about age. It's about God. He lifted St Rita up and put her inside the monastery - he can do the same for you (although He might not make it quite so dramatic for you ). Nothing is impossible for God. Find your spirituality, then your community, then take time to get to know them. Miracles do happen.