Hello and welcome!!
I think "beachalice" provided a great synopsis of the criteria that agencies, perspective IPs and REs look at before qualifying any woman as a potential GS.
Without a doubt it will likley be a challenge at this point even if your health is steller and your pregnancies uneventful. I speak from expereince as a GS who matched at 43 and just delivered my first surro baby at 44 this past Sept. Most agencies do have a cutoff age between 38 and 40 with 42 being the top of that acceptable range. Now there is always exceptions based of course on medical/psycological eval. and wether or not all parties are comfortable working with a women in this age bracket.
I actually began my GS journey when I was 39. I was accepted, matched, and went through too transfers at 40. The 1st although successful ended in a miscarriage at 5 wks and the second a BFN. I revisited surrogacy several years later at the age of 43. I think I had a leg up since I had already been through the process. I was accepted by a different agency and RE, matched and became preggers after the first transfer Jan. 2016. My pregnancy went perfectly as it had with all three of my own kiddies. Non the less my age certainly came up at every prenatal visit. Since age can bring along with it increased risks such as high BP, preclempsia, GD, IUGR which I actually expereinced and with the fetus presenting in a breech position which I also had...REs and OBs alike will understandably consider these issues when deciding upon your qaulifications.
Another point to consider is how much time has lapsed since your last full term pregnancy. Many REs prefer a potential surrogate that has had a healthy pregnancy/birth within the last 5 or so years. Certainly not a requirement but if your age is above the threshold and your last pregnancy was say 10-15 years ago that may be another hurdle to jump over.
With that being said I know there are certainly women on this board who are repeat surros who are over 45 so it's worth investigating.
All the best!!