So what's the age of the other alicorns other than twilight?

[Blu Starset 1]

since luna and cadence are almost similar in height, I can't tell what's their age.

[cider float 2,538]

Cadance probably aged normally, Celestia and Luna are undetermined but definitely over 1000 years old. 

[Chuckles4lyfe 441]

Cadance probably aged normally, Celestia and Luna are undetermined but definitely over 1000 years old. 

 

Agreed. Celestia and Luna are most definitely over 1000 years old since. Remember that Luna was trapped in the moon for that long prior to the start of season 1.

 

As for Cadence, I like to think that she is ~8 years older than Twilight. Think back to when she was foal-sitting cute, adorkable Twily  . If Twi was 6-8 years old, Cadence would be 14-16 (She wasn't a full grown adult in the flashback, but was definitely older than the CMC).

 

Presently, if Twilight is in her early 20's (20-22), Cadence should be ~28-30 years old. Makes sense since this is around the age when people settle down and start having kids  .  

[Unlikeable Pony 2,699]

Cadence I'd put down as about 28, since the comics show twilight being about 8-10ish when Cadence is around senior level age at high school. And I currently think Twilight's probably 22ish.

 

So I think that 28-30 feels about right.

 

Luna and Celestia I'd put down at about 1200 years old; They were found when they were still young by starswirl and alicorns age slowly, so I feel that there was about 200 years between them being made the rulers of equestria and when Luna was banished.