Hello and congratulations!!!
My oldest is 15 1/2 and I had him when I was 25 1/2. I am now 41 and i will have my 7th in January!
My youngest so far are a set of twins--16 months old.
So don't worry---the age gap can be great, actually! Your son is old enough to be fairly independent now, and if anything, I think having a baby can keep you younger, both physically and mentally.
I also know that just through age and inner maturity, I am a lot more calm, patient and understanding parent now than I was with my first and second.
You will probably enjoy this baby more also. I remember with my older kids I was more focused on their academic success, extracurricular activities, trying to be the "perfect" mom, wife, family, etc. But now I am just enjoying watching my little ones just exploring and finding their way around this great earth. I am just enjoying being "present" and not feeling obligated to "do" or to get things accomplished.
I always say that I think of it along the lines of "stopping to smell the roses"----except I refer to it as "stopping to enjoy the babies".
It will be great---even better this time around, as long as you have love and peace inside yourself and your household! :)