“Teaching is easier for someone who knows; not learning first is stupid. ”
τὸ διδάξασθαι δέ τοι εἰδότι ῥᾴτερον• ἄγνωμον δὲ τὸ μὴ προμαθεῖν•

ΕΥΔΟΞΑ ΑΓΝΩΣΤΑ ΚΑΤΑΓΕΛΑΣΤΑ
“Trying is the first step of learning”
πῆρά τοι μαθήσιος ἀρχά
Campbell’s Loeb (p. 481) translates “Experience is the beginning of learning” which sound somewhat better (and better glosses the Line from Pindar). But peira also (and primarily?) conveys the sense of making an attempt or test of something. Any other suggestions?
“Time is the wisest and most unteachable thing.”
σοφώτατόν τοι κἀμαθέστατον χρόνος
(Yes, we left the assertive τοι out of the translation.)
Simplicius, not so simple.

“I grow old but always learn many things ”
γηράσκω δ’ αἰεὶ πολλὰ διδασκόμενος
Solon Nomographos.