I’m not a doctor, but I am over 40 and recently diagnosed. I have been on medication for high blood pressure for almost ten years. When I was given Ritalin, I was told that it *could* raise my blood pressure. So far though, it hasn’t. I’ve been monitoring it almost daily since I started and the numbers are always between 117-109 over 68-82; very normal, in other words. I am still taking my blood pressure meds (I also take Advair, which can also raise BP slightly) and everything is working as it should.
The good thing about ADHD (versus, say, diabetes or heart disease) is that medication is really optional. Medication for ADHD will not save or prolong your life the way those other meds do; it’s just to help you if you feel that you need it. A lot of people on here seem to be managing just fine without the meds.
As far as getting a diagnosis is concerned, the only real reason I can see for getting it at this point in your life is if it’s going to make you feel better about yourself. In my case, having the diagnosis gave me validation. It allowed me to believe that I am not just a lazy underachiever.
I chose to take the medication for the same reason I sought a diagnosis: I was having great difficulty concentrating at work and I was getting really nervous that I was going to be fired. Once I started the Ritalin, it was like someone flipped a switch and I was suddenly able to focus on the task at hand. The first two days I took it were the most productive work days I had had in a very, very long time.
Because of the nature of the way ADHD meds work, it’s not like an antidepressant that you have to be on for months. If you get the right one, the effects are immediate and dramatic. I can foresee myself stopping the meds at some point, but for now, I’m enjoying the creative beast that has been unleashed.
You can get the diagnosis (if you want it) and not have to take medication; no one can or will force you to. Good luck! 
PS Sorry if this post jumps around a little–can you tell that the meds have worn off? 