Canon law is cited for the celebration of First Eucharist. But this section is not without problems.
[87.] The First Communion of children must always be preceded by sacramental confession and absolution.[Cf. Code of Canon Law 914; S. Congregation for the Discipline of the Sacraments, Declaration, Sanctus Pontifex, diei 24 maii 1973: AAS 65 (1973) p. 410; S. Congregation for the Sacraments and Divine Worship and S. Congregation for the Clergy, Letter to the Presidents of the Bishops’ Conferences. Episcoporum, In quibusdam, 31 March 1977: Enchiridion Documentorum Instaurationis Liturgicae, II, pp. 142-144; S. Congregation for the Sacraments and Divine Worship and S. Congregation for the Clergy, Response to dubium, 20 May 1977: AAS 69 (1977) p. 427.] Moreover First Communion should always be administered by a Priest and never outside the celebration of Mass. Apart from exceptional cases, it is not particularly appropriate for First Communion to be administered on Holy Thursday of the Lord’s Supper. Another day should be chosen instead, such as a Sunday between the Second and the Sixth Sunday of Easter, or the Solemnity of the Body and Blood of Christ, or the Sundays of Ordinary Time, since Sunday is rightly regarded as the day of the Eucharist. [Cf. Dies Domini 31-34] “Children who have not attained the age of reason, or those whom” the Parish Priest “has determined to be insufficiently prepared” should not come forward to receive the Holy Eucharist. [Cf. Code of Canon Law 914] Where it happens, however, that a child who is exceptionally mature for (her or) his age is judged to be ready for receiving the Sacrament, the child must not be denied First Communion provided (she or) he has received sufficient instruction.
I’m aware Holy Thursday is a thought for First Communion, but I’ve never experienced it celebrated on that day. What do you make of the explicit recommendations for Easter Sundays 2 through 6, Body & Blood of Christ (still on Thursday in some of the world) or an ordinary time Sunday?
Note the wording: a priest “should” administer the Sacrament. Do you suppose the CDWDS envisioned under the form of Bread only? To my knowledge, the priest nearly always does this. This would be putting a logical practice in writing for the first time that I can remember.
While I don’t have a problem with the insistence on catechesis for Penance before First Eucharist, the insistence on actually celebrating the sacrament isn’t without problems. It may well be the best available solution in the present day. But it remains a sacrament with perhaps the least mature preparation for the laity, and that of necessity. I know of few catechetical or liturgical resources that supplement formation for Penance with age-appropriate content for pre-adolescents, teens, or young adults.
The age or reason is a guide, it seems, that a parish priest might circumvent for a person not ready or prepared, or for a precocious child. I wouldn’t object to First Eucharist for infants, after Confirmation. But that approach seems to have lost some steam over the past several years.