I don't know exactly how old. I think it depends on how commercial the hashtag is. I ran a IG about tech (PC hardware photos), and it took me over a month last year to get constantly on the hashtag searches. Any hashtag about pc parts is considered commercial so maybe that's why.
But for lower competition it can escape the hashtag sandbox or whatever it is in under a month.
Now I don't know how IG does their ranking, because some new accounts, when it detects a virgin IP address or something like that, do get one hashtag outt here just for demonstration, or to wet the appetite. But if on the next post you add 2 or 3, they'll probably be seen by friends but not in the general search.
Well it's simple to test really, just create another account and search for your hashtags and see. I've done extensive tests on FB and IG with this. As I said in the reply to eve121 for a Pc hardware IG it took me over a month to appear normally on hashtag searches.
Like I said, create your own hashtags nobody has used and test. I often noticed that even hashtags with no value whatsoever took a while to get into their search for a new IG account #mypillowandthedog or something like that with zero commercial value.... I think they've migrated the Facebook algorithms to IG.
