Dans le Littré, on trouve ceci :
OPTATIF, IVE [o-pta-tif, ti-v’] adj.
Qui exprime le souhait. Plût à Dieu ! est une formule optative.
En grammaire, mode optatif, ou, substantivement, l’optatif, mode qui, dans certaines langues, par exemple en grec, exprime le souhait.
XVe s. ♦ Nouvellement, par maniere optative, CH. D’ORL., Rondel 68
Prov. optatiu ; espagn. optativo ; ital. ottativo ; du lat. optativus, de optare, souhaiter (voy. ⤷OPTER).
Regarding a possible grammar lesson/connection, M Jean Molinet seems to be giving a recitation of the verb moods/modes that existed in his time (apparently the optative and conjonctive have both been subsequently supplanted/replaced by the subjunctive according to CNRTL).
He seems to be using these verb modes to describe different aspects and moods/attitudes of his life, beginning in the past (signaled literally with passés) in the indicative mood to tell how it once was and finishing in the/[his] present (signaled with maintenant) in the “optatif/(aka subjonctif),” or “wishing” mood to tell how he’d like it to be [with references in between to the imperative mood, the conjunctive/(aka subjunctive) mood (signaled with the old spelling conjuntif), and the impersonal/infinitive mood (signaled with infiniment)].
(To take a stab at one of the questions raised in a comment, although based purely on psychological (and not grammatical) grounds, I’d guess that he preferred to end on a hopeful note and in a hopeful mood.)
On another point unrelated to grammar, with my admittedly anglophone ears I “hear” some wordplay with “vin tant” for “vingt ans” in the last phrase, where he’s perhaps saying that he would ‘just’ like to return to the good age of 20 (je veux seulement [d’]avoir [un] bon vingt ans).
[If my anglo ears are deceiving me and there is no relevant phonetic connection here between “bon vin tant” and ”bon vingt ans,” maybe “tant seulement” is referring to how much love he used to get as a younger man & he’s saying he’d be happy with just as much good wine (“tant seulement”) as he used to get love and that he’s not asking for more than that (“tant et plus”) (but see “tant seulement” at items #30 and #21)].