[Souvlaki]

It don't think it's possible but if it was i guess it would be like this:

pawn Код:

ShowPlayerDialog(playerid, 2, DIALOG_STYLE_INPUT, "Registration Step 2 - Age", "INVALID AGE. 16-60 ONLY\n\nHow old are you (enter your age)?", "Set Age")

Edit:

Wiki:
The text on the right button. Leave it blank to hide it.

pawn Код:

ShowPlayerDialog(playerid, 2, DIALOG_STYLE_INPUT, "Registration Step 2 - Age", "INVALID AGE. 16-60 ONLY\n\nHow old are you (enter your age)?","Set Age",)

Maybe?
I hope it works.