Given that you will only have 5 year age gap, and your partner will be delighted, I think this can be counted as a blessing.
You're not too old (your body clearly doesn't think you are!), and attitude is everything. I had my last at 43.5. It was a very easy pregnancy, and I have never been asked how I cope, if I regret it, or if I'm his granny!
There are plenty of much younger people who aren't active parents, and don't lead particularly healthy lives. Will they be around for their children for the next 50+ years? My neighbour is around 30, and has 5 children. She is overweight, has health problems, and just can't keep up with her children at all. Frankly, I can't see her making old bones, and I at 53, am quite likely to out-live her. Having kids younger does not make you a better or more suitable parent.
In your shoes, I would be looking to have a CVS done if you can (will probably have to be private) as it will quickly show many of the age-related/chromosomal issues that can severely effect a baby. I had it done, and it was easy, not painful, and gave me real peace of mind