We're all Boro fans and I think it's unfair to discriminate against people who weren't old enough to have a Gold Card and shut them out. I also think it's unfair to those season ticket holders who had been waiting for more news before renewing only to find the door slammed shut unexpectedly, only to learn later (like festas_shin above) that some managed to sneak in via a glitch without it being publicised to all. I know those who renewed via the glitch will feel this is wrong but the club have to cancel those sales (or allow all ST holders to renew) or risk alienating thousands of season ticket holders who weren't aware of it and missed the opportunity, it's just not fair, all ticket holders should have equal opportunity to attend through an official publicised process.
The fairest way would have been giving a final renewal deadline to all season ticket holders (GC and all) irrespective of length of holding the ticket. Then the club know exactly how many SC holders want to attend games next year. They all go into a ballot for tickets, you could ask for individuals who sit together to be grouped together like say the Wembley or Eindhoven tickets were so you don't get a situation where a Dad gets a ticket but a son doesn't and it also allows for bubbles to be formed.
In an ideal world you'd have different ticket holders going to different games, so all season ticket holders get to at least see some games live. This might prove logistically difficult though, the only way I can think of is grouping bubbles so in say match 1 a bubble of 4 sit together, in match 2 all other groups of 4 who missed out in the match 1 ballot go into a draw to replace the bubble of 4 from match 1 and take their seats. This way the stadium configuration for social distancing can remain broadly the same but different groups get a chance to attend together. However I accept this may slightly increase the risk of the virus transmission due to more different groups of people attending different games and coming into contact.
I understand the EFLs position on streaming but there has to be some option for streaming season tickets to allow people who can't get in stadiums to see games. I'm not sure how the revenue streams are split and what percentage of the £10 match fee for a stream goes to the club, but surely extra sales of streams must help clubs increase their revenue and help them stay afloat in difficult times? I'd have some streaming season tickets with a bundled price that gives you a discount over paying the £10 match to match fee, say £150 - 175 for a 23 home match season. Season ticket holders who miss out on a game ballot get this for games they miss seeing in the stadium.
I say all of the above as a GC holder, but I think fairness has to win the day on this one. As festas_shin says above missing out via an official equitable process might be disappointing but understandable, but to miss out due to essentially not hearing a sneaky underground whisper is just not right. The club need to do it properly and above board or risk p*ssing everyone off.
