Hello aspirant

hope you are doing well and safe. With reference to your query,  I would glad inform you that you surely join allen from class 11th but in my opinion you should continue only from 12th if you are highly confident on concepts you have learnt in 11th because when they take mocks and teach topics in which 11th concepts are applied then you will face difficulty so work accordingly

Hope you found this answer informative. Best wishes for your future