Q. Can you give a Bar Mitzva or birthday present that was already purchased before the 3 weeks? Thanks.

A. On a prior answer we wrote: “Shulchan Oruch (O.C.551: 17) rules that it is better to abstain from reciting the blessing of Shechecheyanu during Bein Hametzarim (the three weeks). Mishna Berurah (ibid. 98) in Magen Avrohom name explains, that since these are days of desolation, it is improper to bless in them that particular brocho”. It is indeed unlikely that someone would recite Shechecheyanu over a Bar Mitzva or birthday present.
Mishna Berurah (554:41) prohibits sending a present to a friend on Tisha Beav. It would seem that on the prior days it is permitted. However Mishna Berurah may be referring to a gift that does not generate Simcha, and is only forbidden because of the ban on Sheilas Sholom or greeting in Tisha Beav, where this particular halocho appears.

Darchei Hoiro’o (p.39) permits giving during the nine days, Bar Mitzva presents or gifts to a teacher at the end of a school year.

Horav Shlomo Miller’s Shlit”a opinion is that prior to Rosh Chodesh Av it is permitted to give presents. But during the nine days one should abstain if possible, and wait until after Tisha Beav.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.