I started to change my diet on the 30th Dec last year, I'm now in week 7 and I haven't ' slipped ' yet.
I'm approximately in your age, height and weight range ( although a few years older, and about 30 pounds lighter ) and I'll tell you what I've found to be true for me ( and I'm no expert in success but I have tried and failed to change so many times that I've actually come to realize a few things ):
I'm not trying to lose weight for the Summer anymore. I intend for it to be a permanent change of lifestyle that will continue from here on in. I cannot emphasise how important it was for me to really wrap my head around this most basic of concepts. It took me years.
I don't rush to results. It's a war of attrition and I just need to ( forgive me ) ' weight ' it out. I'm in a caloric deficit, weight training ( basic stuff but doing it consistently ) and losing weight while getting stronger day by day. The results will come, I know this and I just have to be patient.
I should have done this ten years ago. I have aches and pains now that are always with me and it makes this harder. But if I wait another ten years? That thought terrifies me and I'm going to keep moving forward with this NOW.
Like I said I'm only in week 7. I look at the people on Reddit who post their year long transformations and while it is inspiring it's also daunting because I'm not them. I still have it all to do but if it's a life long change then so what? I'll get where I need to be eventually.
You may have reasons that are specific to you that you think will keep you from achieving your weight loss goals. I know I have mine and depression can make you believe that you're not good enough to do this thing, not worthy somehow; that you're going to fail because you always do so what's the point in even trying? I take all that negative shit and I challenge it to make me stop my diet, stop me exercising today and as lon as I keep dong what I'm doing it holds no power over me.
I'm going to work out now because I want to take another positive step towards a better life. I hope you choose today to change like I did. It ain't easy but I KNOW that it will be worth it for you the same as I know it will be for me.