There was supposedly a sourcebook whose name escapes me that pegged X's mental age at about 14 in X1. The implication is that this can increase.
Following from the above, this is actually a somewhat difficult question for a very stupid reason.
That reason is this, regarding Xtreme 2:
View attachment 6082620
Based on this, the answer is "yes during Xtreme 2, unknown as of X4 because she somehow hit robot puberty."
Everything else is after-the-fact supposition. TEPPEN cards relating to her X4 appearance use Japanese words that typically describe young girls, such as 少女. Part of the change to the more adult-looking Iris Another in DIVE includes a deeper voice done by the same VA. In DIVE, X4-era Iris and Zero have the same interaction Zero does with Ciel as I have described before, when Ciel starts at 14 in Z1 and maxes out at 16-17 in Z4. Zero fans not on the fujo end often tend to see Ciel as a kind of Iris replacement.
So, draw your own conclusion.