Whatever age you want you are an adult being 24 right?
I was 25 or so when I started gaining and my Mom still doesn't like that I made myself fat and I'm 47 now.
Chances are they will always comment or say something so just get used to that.
The trick is to not pay attention to their comments about your weight.
Certainly don't wait for them to die off thats kinda creepy.

Ok you go ahead and challenge yourself.
I'll watch your gain from the sidelines.
I have been there done that years ago but if you need tips along the way feel free to ask.
I do need to ask have you ever done this before?

I did something like that when I caught my first husband cheating on me with a very large woman.
I was maybe 115 lbs at the time so being his trophy wife if I didn't look hot all the time he would get mad.
After I caught him I stopped doing my facials and taking care of my hair and that was when I first tried to gain weight. I figured he wanted a big woman so I was going to get big and sloppy just for him.
Stopped wearing sexy cut off jeans and shorts and started wearing styles more like my Mom wore.
Stopped washing my hair as often which caused some acne to form on my face plus not washing my face daily helped that along too.
I started letting jeans get more dirty looking by not washing clothes as often.
I did manage to gain about 60 lbs and looked pretty awful before he finally filed for divorce.
That all changed after it was final.

Whats the point?
Its not going to make you gain weight that will stick and just make you get severe indigestion.

Welcome back Bonnie.

Seems the problem is self motivation so fix that problem and you won't need to make a challenge.
Chances are you aren't going to do the challenge anyway because you don't have the will.
Why do people say they will do something when they know they aren't going to do it?

I think its OK for you to explore your sexuality and your desires.
I felt that way about chubby and fat girls/ women. Feeling their soft plush bodies rubbing mine and how exciting it was.
Enjoy exploring.

OMG yes I love it !!
I loved to wear a top just a size or two too small so my big flabby belly would peek out and jiggle when I waddled along pushing my grocery cart.
Sounds so silly I know but it was exciting for some reason.
When I first started to get a muffin top I wore crop tops all during the summer letting my fat hang out.

I have gained a bunch then lost 80-100 lbs and gained it all back several years later.
Never really thought about it but I did enjoy the process of gaining it all back and fitting in my old fat clothes.

One tip I can give don't get on the scale every day expecting to see more weight only to be let down.
When I was a gainer I stepped on the scale on the last day of the month to see what I had gained that month.
Its better to be surprised than let down.