I agree the nice thing about Aikido is that there is no single body type or personality. This is one of Aikido's strengths.
I would suggest that if you maintain a good level of training with sensible eating you'll find the Aikido will change you rather than you changing to the Aikido.
Saying that, I'm comming back from from a long layoff and What I can tell you is the heavier you are the harder work it is. Not that I was ever that slim!