Are my prayers and ablutions for 15 years after puberty invalid due to my ignorance of the correct method of istinja' (washing after urinating or defecating), and is it sufficient to wash only the glans of the penis, or must the entire penis be washed?

The answer included several points: 1. Urinating while standing is not disliked if there is an excuse, but it is disliked without an excuse according to the majority of scholars. Washing the feet or bathroom slippers is not necessary unless the presence of urine splatter is confirmed. 2. It is not necessary to wash the lower half of the body after defecating; rather, washing only the affected area is sufficient until the removal of the impurity is predominantly believed to have occurred. 3. Washing only the exit point of urine is sufficient, not the entire penis. If the location of the impurity is known, only that specific area is washed. 4. Wiping the impurity with a tissue or similar item is sufficient, provided it is not less than three wipes according to some scholars, or until cleanliness is achieved, even if with fewer than three wipes. Using water is better than wiping alone, and combining both is best.

Therefore, your previous purification and prayers are valid, and you do not need to repeat them.