Although Neuro-Sama and Evil have different birthday days, they are twins. Why? Because Evil-Neuro have Neuro-Sama memories from the point before she started to have her own identity, so in terms of memory she is the same age as Neuro, but in terms of identity no.
#Lore or explanation on twins thing and birthday days
latent junco
dense yew
again there is no "lore" really 
mellow solar
More clones than twins imo
latent junco
again there is no "lore" really <:cupsama:1109248605577023599>
That's the why of the "or" in title.
Explaining in the most neutral words I can: the other set of memories plus LLM prompted to be "Evil", we call all this "Evil Neuro", have in part of her set of memories the same memories as the other set of memories of what we call "Neuro-Sama".
So technically both have the same amount time of "experience of things", like clones (as the interesting suggestion of @mellow solar).