although I am a windows user - I also have had ipads and have an iphone presently. (current machines are a lappy running win 10, Microsoft surface Pro 3 (win 10) and Iphone 6 plus).
It is difficult to know how much he will use it --------- but, if it is just very basic use - and first time -
I would have to say that there is no more intuitive machine on earth than an ipad or similar - not android - apple is far more intuitive - that was Job's forte.
I would try and nut out first where he might use it ------ on a table, on his lap - in bed etc. etc.
I would not fall into the trap of going cheap at first necessarily - because often - cheap can spoil the game - like say - taking someone for a drive in an old Tojo - compared to giving them a drive in some quiet, auto, climate control, powered ashtrays etc. - you want to entice them - if you get my drift.
If you think you can manage to get him onto say windows - then either a lappy or MS surface (Pro series) - would be good ---------- something that loads like a flash - rather than click and wait for your next birthday.
Also - really really important ----------- anyone needs something to do with a tool --
ie. no point in learning to use a hammer - if you don't have something to build - there just is no incentive.
So - any personal interests he has - are almost odds on to have some application on a computer - even if it is just keeping in touch with others.