A wise man once said 'don't stick your d**k in crazy'.
'Unless you're a 6 foot ant capable of subsuming genetic powers via ingestion of blood and are a one-man-army, in which case go for it.'
16 is fine since your MC is 16 as well. Mental age doesn't work the way you claim it does either, if anything his mental age would have regressed closer and closer towards his physical age.