As we age is it harder to fall in love?

I’m 40 – I’ve been single for 3 years.
Every relationship I’ve entered into, which is 3, has never worked out.
I’ve liked the guy, never fallen any deeper and the intimacy was always forced on my end. I never enjoyed it and the relationships always ended, and I was fine. Now I’m dating a man, I have a child and so does he which I love, he has a great job and I’m slightly attracted to him. Yet, I can’t be intimate? As soon as it comes time for the intimacy part I shut down, I don’t want to be touched and I start feeling really uncomfortable. I want another child so it’s really important to me that I feel that connection. I’m starting to think that something is wrong with me. I love being on my own with my daughter. I’ve been that way for 3 years, is it possible I’ve lost the ability to love? Does that happen? Could it be a disorder? Attachment disorder? I’m really scared that I’ve lost the ability to be intimate, to feel butterflys in my tummy and I will be alone forever.
Sounds dramatic but I just want to meet someone that I can laugh with, have fun with and perhaps have a baby with. Yet all the men I’ve dated so far, whilst being initially attracted to them, they never work out as I just shut off. Any thoughts?