Is 40 to old to have children?

Maybe,maybe not. Many women are quite successful in their pregnancies at 40.There is some reduced fertility & increased risk of complications, but if your basic health is good & you understand the increased risk of down syndrome, i don't see any reason to say it's too late.
Usually, no. Only safe, "generic" answer is that you should decide this in conference with your gyn dr after an assessment. (and your partner, of course.) as women pursue advanced degrees and career standing, pregnancy is routinely falling into the 30's and sometimes 40's. It's what is safe / healthy for you.