If you are in a financially stable situation and are trying to convince your husband that you need to get pregnant before you get too old, the magic number often quoted is 40. After that, the woman's eggs are older and the risk of Downs Syndrome goes up.
It's funny to be talking about money when you asked about age, but I've heard from too many teenagers lately who think having a baby is just peaches and everything will juat take care of itself.
And your relationship has to be mature. It can be tough on a marriage to raise a child, even sweet and wonderful kids can put inadvertent stress on a couple. It's great to know each other really well, and to have solid confidence in each other.
That all said, I do think you have to be sure you have the money well in order or it will be a BIG problem if you have a kid or kids. Essential financial stress increases all other stress. "Enough money" would be having a place to live that you like, a solid job (and enough skills, should you lose it, to get another one), good insurance (especially health insurance! but also life insurance and disability), workable transportation, and an emergency fund. I put the financial solidity somewhat before relationship solidity because while I think a financially stable single mom can do a pretty good job of raising a child, I think a financially unstable couple will have a lot of stress.. Love is great, but it doesn't pay for food, babysitters, and braces.
My bit thing with having kids is being financially in a really good place. college should be finished, careers started and going strong, etc. Relationships should also be solid with a couple having some history together so that they will go the long haul and the kids can have a two parent home. I would say for most, to be anywhere near that criteria, they're going to at least be in their late 20's. But I've found that my kids require much from me. I cant still be working so much on myself when I'm trying to guide kids. I want to provide my children with every advantage and really, in this world, that is often what it takes. Sadly, kids born into poverty stay there their entire life and repeat the cycle themselves and it is unfortunate. So, you don't have to be rich but you have to be financially stable. Emotionally stable as well. Mature. Ready to put something before yourself and sacrifice for them at all times.
good luck
I don't think this question can be answered with a number. You and your husband/wife should be mature, as well as physically, emotionally and economically stable. If its a big struggle paying your rent, or have to live with others, having a baby is not going to make your life any easier.