New to Rays couple questions

[Askaleymanfish]

So just got a ray today it's a motoro not sure of what kind tho Ima be postin a couple pics in a lil while when I get it in the tank .... But how do I tell how old it is ? It's about 6-8" around the store said they have had it for about 2 months also what is the growth rate I should expect with Motoro Rays I know how big they get but idk how fast they grow and does anyone got experience keeping them with bichirs ? I have 2 bichirs between 12-15" that will be its tank mates

 

[Askaleymanfish]

Here is some pics if someone can tell me the type he is to

 

[Ihsnshaik]

Looks like a standard motoro. My motoro is 4 months old and Aprox 6". Mine grow pretty quickly and I know it's 6 inch because I have a round clay disk exactly 6" and it likes to go on top of it and lay there haha