I have a Global Elite(GE) friend told me that when you play matchmaking(MM) and you start from T side, this mean that your team ELO is higher than the enemy, and if you start from CT side, your team ELO is lower than the T side. Is that real?
No, it's random.
ELO ratings do not have anything to do with that. You could play the same team twice and still end up on CT, even after you've won the previous game starting on T.
Source: Personal experience.