Well I voted 3.5 also. But when I say this, I almost need an asterik * . I don't believe they are truly mature until 4 I think they have to live through that 3rd rut. There are so many expiriences to be learned,and thats what these deer are doing learning!
Look at the trail cam thread, is that not a conditioned responce to avoid a trail cam. I have 1.5 & 2.5 year old deer that I think run to the camera to get their picture taken. Yet the 3.5's vanish from film.

GMMAT said it if we take the 3.5 out of the equation the number drops big-time...Why? 2 reasons there are way fewer 4.5's because alot of "smart-ones" died at 3.5 trying to mate....and many,many dumb ones, who died before that!