[AngelicaDeAlquezar]

I don't think we make so many differences; we don't seem to care about how close we are to what "side" of the decade.
As Poli said, if we don't want to tell our age or want to guess someone's age, we'll normally say: "tengo treinta y tantos años"/"tiene unos treinta y tantos años".

Side note, when someone feels too old to avow their age, they may say "treinta y pocos" (for example), as a humorous way to mean they aren't too close to the next decade.

Same for the other decades: "veintitantos", "cuarenta y tantos", etc. That's always vague enough to avoid disclosing one's exact age.