'marriagable' age

so what is the best age to get married? i just gotten news from my bro that one of ours distant relative had proposed to his gf, but the thing is he is just 1 yr older than my bro. my bro is 23 this yr. they are going to ROM this november, think customary can wait. are they too young to get married? my bro thinks differently...he says is ROM only, still dont need to stay together, so dont need to worry so much. but what is the point of ROM and only doing the customary 2or 3 yr later? the feeling of newly wed will be gone...for me the time to get married is the time when both of you are financially stable to start a family. right?