From an objective point of view - it doesn't matter when it happens, it matters how it happens and with whom. Love and romance is essentially anything but a numbers game and it very much matters that both you and your partner are comfortable with everything and that the whole experience feels and is special. This will only happen when you find someone right for you - time is not of the essence here as much as you'd think.
From a subjective point of view - Buy some Whey protein powder and start drinking it daily, subscribe to a Gym membership or buy a set of cheap weights to use at home. Eat more protein as much as you can - eggs, rice, chicken, cottage cheese, to name a few. Add a few mass-gaining foods such as beef and oatmeal and you have a way towards a more muscular physique which will not only give you more confidence, but also more attention from others. If you're not doing it already, start dressing in a casual, but smart way - shirt with a sweater on top, some nice jeans as well as maybe a blazer from time to time if you're going out. Start making friends with girls no matter if you're interested or not - actually engage with them, treat them like actual people, nice and friendly, but not desperately so. When you meet someone you like, give them a compliment from time to time, take time to actually listen to what they have to say, casually engage in some physical contact and make it known you're there for there for them, but actually have other things to do and other people to meet. Act like yourself, like you otherwise would, just in a more calm, relaxed and engaged manner.
Good luck.