3D sexing scan!

Hello all you lovely people! I would just like to know how many weeks must you be to go for a 3D sexing scan? When I had my second son which was nearly 5 years ago I was told 16 weeks, my first son I waited till I was 20 weeks with my normal hospital scan but I have just seen that it can be done at 14.5 weeks! Please everyone let me know if you have been told any different ☺️ thank you