I think it entirely depends on the person and the circumstances.
As can be seen by many of the responses, typically, the posters saying "too old for them" have already had children.
If you've already had children by 38/39/40, it's likely that you may feel too old for them. However, if you haven't and want to, you won't or you're prepared to deal with all that comes with being an older mum.
Yes, there are statistics that show that the older you are, the harder it may prove to be to conceive and the higher risk the pregnancy is. However, those are just statistics. Important to bear in mind, but not get too bogged down with to the point of allowing it to paralyse you.
Speak with your healthcare provider, follow their advice and get yourself into as healthy a position as possible and just keep trying. Women are having children later and later, and so, our understanding of fertility at those later ages should grow.
There will be examples on each side of the aisle regarding this. Those who have struggled to conceive when they're older (and maybe faced other complications, and those who conceived with no issue and had perfectly healthy babies. Likewise, there will also be those who are in their 20s who struggle to conceive, have babies with chromosomal abnormalities or miscarry.
Age is just a single factor. And I'm also in your boat-I'm 35 and wanting to start TTC soon.