It took me years and many different dedicated partners and still I didn't think that I had reached an cllmax. Then about 2 years ago ( I am 34) I started using a very strong massager type vibrator and can bring myself very quickly to cllmax during sex or masterbation.
I tried all that advise about masterating myself and comunicating with my partners and being selfish and being on top and etc and none of it ever worked. I never got anywhere. Regular vibrators didn't do it for me, I tried lesbian sex etc etc.
My advice is to try as many things as you can. Go to a sex shop talk to some of the girls there and ask what often works for other people and try it yourself.
My husband is a little sad that it is not him alone that is bringing me to cllmax, but he would rather I had one and is there for willing.
Just so you know I was convinced that I just couldn't have them or was not knowing them when I had them.