K.A.
Just because you are older does not guarantee that anything is wrong. Even with the higher risk when you get older, it's still a very low chance of anything being wrong.
Personally, I wouldn't do an amnio unless other tests show problems. Do the ultrasound to look for markers. You've already done the blood test which came back with a negative. Amnios come with risks. When I had one done while pregnant with my second child I started having contractions and ended up on bed rest all weekend hoping I wasn't going to lose him. Thankfully the contractions stopped and all testing came back negative and the issues that came up on the ultrasound all resolved themselves before he was born and he's perfectly healthy now after being born full term.
Just relax. More pregnancies are perfectly fine then not.