Learn Farsi: تجربه‌ی او بیشتر از تجربه‌ی من است.

بیشتر is the irregular comparative form of زیاد (much/many) or بسیار (a lot). While it literally means "more", Farsi treats abstract nouns like experience (تجربه) as a quantity that you have "more" of. In English, we often translate this natural Farsi phrasing as having "greater" experience.

Why is there an extra ی attached to the word تجربه in تجربه‌ی او?

The word for experience, تجربه (tajrobe), ends in a silent 'e' sound written with the letter ه. When you use the ezafe (the grammatical connector meaning "of") to link it to the pronoun او (he/him), you must add the consonant ی (y) as a bridge between the vowels. It is pronounced "tajrobe-ye".

Doesn't the word از mean "from"? Why is it used in this sentence?

Yes, از typically translates to "from". However, in Farsi, it is also the exact word used for "than" in comparisons. Any time you use a comparative adjective like بیشتر, you will use از to introduce the thing being compared against.

To avoid repeating the word "experience", could I just say "his experience is greater than mine" using a single pronoun?

Absolutely! This sentence spells out "my experience" (تجربه‌ی من) for clarity, but just like in English, you can drop the repeated noun. It is very natural to simply say (literally "his experience is more than me/mine").