Babylon (B), 2nd step: Can you use this ability only one time?

Question

The wonder Babylon (B) has a special ability on step 2: You can play your last (7th) card instead of discarding it.

These two questions cover if you'd have to play both cards in the 6th round or if you get a 7th round:

• Can a resource card be used more than once in a turn when allowed to build more than one structure?
• 7 Wonders question about Babylon guild

I wonder: Can you use this ability in all Ages (if built)? Or can you use it only in the Age you built the wonder?

I assumed that you can use it every Age, but then I noted that the special ability of Olympia (A), which can be used in all Ages, has "I, II, III" written on it. This clarification is missing on Bablyon's (B) second step, though.

Answer 1

You may use it once per age. The description of symbols page shows that symbol as (emphasis mine).

The player can play the last card of each age instead of discarding it. This card can be played by paying its cost, discarded to gain 3 coins or used in the construction of his or her Wonder.

Answer 2

I'm certain that you can use the ability in all Ages. I would expect some kind of gloss such as "Once in the game, you may..." if this wasn't the case.

I wonder why Olympia should have a special clarification though. Perhaps it is to make it clearer that you can only build a free building once per Age (i.e. I, II, III to imply a maximum of three free buildings). There would be no need to worry that a player might try to play their last card more than once per age, of course...