Please reconsider advanced jobs starting at the same rank of its parent class.
I'd be fine with them unlocking at 30 or 20 but you'd be able to level them from that level and up.
With the upcomming exp changes and the ones we got already, getting to 50 is already inceridbly fast and besides what little end game content we have, there is barely any group content to partake in.
Having to level adv jobs up would be a great idea so I'm not sure why this path wasn't taken.
While some might call it a timesink, if you dont enjoy leveling aspects in a rpg then perhaps you're playing the wrong genre.
One of the charms of playing FF online games is that you can experience every class/job/storyline with making just one character instead of making 10 alts.
Having jobs start at 50 (in general most players have 2-3 50s) or whatever rank your class is at the time of unlocking would be like missing out on half the job, at least for me leveling up a class/job is half the fun, its progress and character development, one of the key reasons to play a mmorpg.
One thing a MMO should inspire to give is the feeling that there's always things to do, if you feel you have done all that the game has to offer, then the MMO is simply lacking.
Again take a look at XI with its multiple classes/jobs, and in that game leveling to cap (75) took probably at least 10 times longer then leveling to 50 in XIV and it had 21(or more?) jobs to choose from.
When I log on I want to think "oh what should I do today, i have so many options!", in XIV I constantly get the feeling of thinking "ok I shouldnt' level x class cause then I wont be able to experience it leveling as its advanced job" and this is from playing 1-2h a day on average...
I'm fine with the game having casual elements to it, but even for casaul play there should be things to do, and simply pumping in handfulls of random NPC quests, escorts ,events and sparse end game content every 2-3 months will not be able to keep up with how fast players go trough it.
Sorry for the long post and I know this probably wont change the implemention of the advanced jobs, but voicing my opinion to let devs know what I'd like to see in their game is one of the reasons forums are here.