I'm so embarrassed

-- Sorry about that
The flameback as far as I know, only shows sexual dichromatism during the mating itself, by then you've already accomplished your goal.
They get up to about 3 inches - maximum. How long is yours from nose to tip of tail? About the only thing I can think of to go on is that if its fairly large and you've had him for more than a year, without the presence of other angels, there's a good chance he's a male.
The main thing though is to find a fish that is m-u-c-h smaller and and an obvious juvenile
The best way IMO is to set up a quarantine tank with some LR and even better, if possible , macros - C. acanthops loves macros. Buy your teeny one and let her acclimate in there for 2-3 days, then catch your "male' and add him to the quarantine tank. You'll know right away if they are ok, but expect some chasing. If the female must cower in a top corner of the tank, then it's probably a failure - you can give it a little time if he's not physically hurting her, but the longer this goes on , the more likely she is to succomb to disease from the stress.
Actually it's the better way for the flames, too. I was thinking in terms of favoring the 10 year old fish and not wanting to stress him by this extra moving around.
.HTH