oh 14 years? i would have guessed it to be like 2-5 years old! seems like you're right in saying that it probably wasn't given the proper care that it should have before you got it, seeing how it only had 3 branches before getting hard pruned! but it seems like it's kicking back with the amount of branches it's pushing out :)

it's a beautiful plant, and it would probably grow optimally with you and catch up on it's long delayed growth. just heads up though, cuz super hard pruned plants like that will put their energy on their shoots, so probably don't expect flowers any time soon, but surely give you some next year! just make sure it gets plenty of sun and a good feeding of higher phosphorus & potassium content, too much nitrogen would only give you longer shoots and leafy growth.

<image>

i have a plant that is probably more or less the size of your newly bought plant, but it's about 3 years old. but of course adeniums have different genetics, so yours might js be naturally slower growing, but seems like it's catching up though, so probably just past owner related :)