"Unable to accept mentor certification at this time."

[ManuelBravo]

Are you sure you met ALL requirements; Note most people usually don't meet the achievement part right a way.
also if your a sprout have to let some time pass by I think until your no longer in that.

http://na.finalfantasyxiv.com/lodest...b5a39c/#mentor

The mentor system provides more experienced players a means to offer advice and guidance to newer players. Mentor Requirements
To qualify to become a mentor, players must first have earned certain achievements. There are two sets of prerequisites, one for Disciples of War and Magic, and one for Disciples of the Hand and Land. After earning the required achievements for either set, speak with one of the Smiths to become a mentor.

Achievement Requirements for Disciples of War and Magic

1. Players must obtain at least one of the following three achievements:

Achievement Requirements
Like a Knight in Shining Armor II Complete the paladin job quest "This Little Sword of Mine."
I Am the Warrior II Complete the warrior job quest "And My Axe."
A Dark Day's Knight II Complete the dark knight job quest "Absolution."

2. Players must obtain at least one of the following three achievements:

Achievement Requirements
Seeing White II Complete the white mage job quest "Hands of Healing."
Flying Colors II Complete the scholar job quest "Forward, the Royal Marines."
The Stars in Our Faults II Complete the astrologian job quest "The Hands of Fate."

3. Players must obtain at least one of the following seven achievements:

Achievement Requirements
Bulletproof II Complete the monk job quest "Appetite for Destruction."
Dragoon Age II Complete the dragoon job quest "Dragoon's Fate."
A Bard's Tale II Complete the bard job quest "The Ballad of Oblivion."
Back in Black II Complete the black mage job quest "The Defiant Ones."
Soul Summoner II Complete the summoner job quest "A Flare for the Dramatic."
Against the Ninja II Complete the ninja job quest "In Her Name."
I'm a Machinist, Not a Man II Complete the machinist job quest "Rise of the Machinists."

4. Players must obtain the following achievement:

Achievement Requirements
Dungeon Master Complete 1,000 instanced dungeon raids or trials.

5. Players must obtain the following achievement:

Achievement Requirements
Leaving a Good Impression IV Receive 300 player commendations.

Achievement Requirements for Disciples of the Hand and Land

1. Players must obtain at least one of the following eight achievements:

Achievement Requirements
Knock on Wood VI Achieve carpenter level 60.
Temper, Temper VI Achieve blacksmith level 60.
The Riddle of Steel VI Achieve armorer level 60.
Heart of Gold VI Achieve goldsmith level 60.
Tougher than Leather VI Achieve leatherworker level 60.
Smiling, Styling, and Textiling VI Achieve weaver level 60.
Tis True without Lying VI Achieve alchemist level 60.
All in Good Taste VI Achieve culinarian level 60.

2. Players must obtain at least one of the following three achievements:

Achievement Requirements
Breaking Rocks in the Hot Sun VI Achieve miner level 60.
Fear the Reaper VI Achieve botanist level 60.
Gone Fishin' VI Achieve fisher level 60.

3. Players must obtain the following achievement:

Achievement Requirements
I Made That (Worth Collecting) I Synthesize 100 collectables.

4. Players must obtain the following achievement:

Achievement Requirements
I Collected That I Gather or catch 300 collectables.

After meeting the above requirements speak to the Smith NPC to register as a mentor.