Topless vs. Shirtless

If somebody asks me to describe the below photo, I would definitely say, "It is a picture of shirtless Putin on a horseback".

The adjective topless is defined by Oxford Online Dictionary:

(Of a woman) having the breasts uncovered: a topless dancer.

And according to Online Etymology Dictionary, topless means:

of women, "bare-breasted," 1966, from top (n.1) + -less.

And I looked up the bold top (n.1) above in the same dictionary and it states:

Few Indo-European languages have a word so generic, which can be used of the upper part or surface of just about anything.

And nothing else to clarify the meaning. However, the headline of The Independent reads:

Chelsea Handler uses topless Vladimir Putin photo to highlight Instagram nudity inequalities

Questions:

1. Can the adjective topless describe a male? What is the difference between shirtless and topless, then?

2. What does the noun top mean in topless? What is its etymology? (I can't figure out from Online Etymology Dictionary.)

3. Are there more apt/suitable words to describe the below picture besides shirtless (or possibly topless)?

Topless was originally used for males. Shirtless is much older. The idea was to indicate that the breast was not covered. I'd use topless only to refer to women, shirtless is used mainly referring to males Ngram:

topless (adj.):

• of women, "bare-breasted," 1966, from top (n.1) + -less. Earlier it was used of men's bathing suits (1937) and women's (1964). Earliest sense is "without a visible summit; immeasurably high" (1580s).

shirtless (adj.)

• c. 1600, from shirt + -less.