I am going to turn 40 soon and am 30 weeks pregnant with my second child. No problems, I feel fine and if I didn't think that 2 was enough, I'd feel quite capable of doing this again.
Your age is merely a number, what matters is how healthy and fit you are. American Indian women had babies into their 50ies, and lived a natural lifestyle with unprocessed foods, activity etc. Exercise and good nutrition, as well as a positive attitude all make a difference.
Janet Balaskas, who founded the Active Birth movement and has written many Yoga for Pregnancy books, had a baby well over 40, more than 10 pounds.
If you eat healthily, your body may even feel younger...
If you want another child and feel fit, go for it! Enjoy!