It is all very easy...
First of all, you have to meet the requirements ( 5000hrs TT, 3 years in company)
Than you take your calculator and you start counting:
500 FOs in company today, all of them more senior than you, most of them will meet the requirements ahead of you. Lets substract 50 to cater for second officers who will need more time.
450 FOs in front of you, awaiting upgrade.
Contrary to popular belief here, there are NO plans being made so far to upgrade on any other fleet but the A320s. and thats a fact!
A320 handles about 4 upgrades/month, 44 upgrades a year maximum!
Of those selected about 60% gets through the upgrade process, others fail.
So if all goes well, you have to deal with 270 FOs in front of you who will make it ahead of you, at a rate of 44/year max. This gives you a time frame of 6.13 years to wait if you would join now!
This is calculated with the situation as we know it today. And we all know things can change in any direction any day around here.
Good luck!